Yes indeed this is an issue, I experianced it first hand, although in my case I played as the Eldar which is probobly the best race to play from that position as they are very capable of fighting on multiple fronts in the early game at least.
 
Its worth mentioning though that one drawback of being in a corner is warp storms, they tend to have greater impact on you when you already have sides that have permenant barriers.  In my game I very effectively cornered people in ways that greatly impacted their ability to take strategically effective actions.  If your more central you naturally have more options as a result of blockading warp storms.
 
Still, the Triad issue in Forbidden Stars has at least for me put this game out of prefered selection for a game night when only 3 players are available.  I haven't tried it 2 players and probobly never will, I tend to want to play games specifically made for 2 players when that occurs.  So really FS is a 4 player game, no more no less.  I think the downtime of combat is acceptable (although on the edge) in a 4 player, but will be too much if we ever see a 5th player added, so I think its forever destined to remain a 4 player game to me.  A great one which I will happily play, but a lot less flexible than I had hoped.

I'm about to play my first game of FS but from reading the rules FS is less an adaptation of Starcraft and more along the lines of "borrowing" established mechanics which is actually a really good way to design big board games.
 
Typically Big Board games (aka complex multi hour board games) that are designed from scratch without basing their mechanics on established games don't work out very well.  This is why often 2nd and 3rd edition games are better than their predescessors as they take what works and re-develop that didn't (3rd Edition Twilight Imperium, 2nd edition descent are some good examples of that in action).
 
Starcraft had a lot of new ideas in it, some that I think are very good, others that fell flat (and actually infected other games that fell equally flat).
 
For example the command actions (stacking commands on top of each other) as a method of taking actions is actually a well established mechanic that works well.  You see it in games like Games of Thrones and of course in Starcraft (one of the things that worked really well in that game) as some examples.
 
Other things in Starcraft like pure card based combat doesn't work that well and we have seen it fall flat in a couple of games not just Starcraft (Sid Meier's Civilization, Rune Wars for a couple of examples).  It just doesn't work that well, it lacks the dynamics.
 
Fortunatly these are the things that FS corrects, for example they brought dice into the game mixed in with the card combat and that is a good idea, it creates those clutch moments and a bit of dynamic randomness that means when you go into a fight, while the odds might be stacked against you, its not a presumed loss based on the available information you have.  I know that Euro gaming really likes that "fixed" pure strategy approach to gaming but it just doesn't work particularly well in games with combat systems.  You really need that randomness to get that dynamic illusion that only randomness can offer.
 
I do see a lot of Starcraft in this game, but I don't think you can say that if you like Starcraft you will like this (or if you didn't you won't like it).
 
One bad thing about extended combat (which Starcraft also had) was that it creates downtime and FS very clearly suffers from extended downtime for players not involved in combat as a combat can take a few minutes to resolve.  How much of an impact that will have on your group and on your experiance I think will be something you will see argued on these forums in the future and you will see "how to speed up combat" threads in the near future if there aren't any already.
 
As a precurser to that argument, something I often say about all Big Board games is that downtime is part of the deal.  Wether its TI3, Games of Thrones or other broad (big epics) along those lines, the time commitment and potential downtime is always there and its just something you have to accept about the game.  Im sure there will be ways to speed it up, most of the time it will come down to experiance with the game but its there and it always will be.

It's inherent in all the images/examples in the rules. If such a movement had been an option, it'd have been stated clearly in the rules. Thematically this has sense: have you ever seen a general commanding to advance, and the troops side tracking a couple of continents before returning on target?
It's true that it's not openly worded in the rules, but rules cannot cover every rules lawyery.And this point is in any case pretty well covered in the rules: you need adjacency to call your troops, but warp storms block movement. Why such rules would have been created if the intention was allowing to bypass the warp storm by strolling around? If this were a legal move, then why not allowing players to move troops from any one system as long as a legal path is available? They asked for adjacency instead, meaning exactly this. No strolling around, but short paths along which to move the army
Then, if you prefer one official answer, you can use the Rules question button on this very site to ask FFG directly

Hey there,
 
even though I just bought this game, I already love it and I'm looking forward to see a lot of Expansions.
 
Still we got the "problem" of downtime the players have, not being involved in battles (like in Starcraft: The Board Game), hope they gonna fix that somehow.
 
Also, while I was playing 40k, I played as Tyranid. I jhust love these typical Starship-Troopers/Zerg-"Aliens". I would love to see them in game as well, but not as a playable faction. I would prefer seeing them taking over the universe on their own (as NPCs) and sometimes players are "forced" to stop them together, before they continue with their objectives. So in some events "Forbidden Stars" turns into a Coop-Strategy Board Game
That's what also fits to Tyranids, just absorbing all planets. U cannot stop 'em alone, but together u might have a chance to last a little longer, before the next swarm arrives.
 
What do u think??