Im pretty new to this but I also thought that the tension meter is a bit strange but got some good ideas out of the discussion
Why start either high or low? With a newly formed party with arbitrary people that doesnt know each other, joining together for a task theres bound to be tension.
I think starting in the middle and be able to both rise and lower the tension from the start would be a better idea. then I think it could become a good tool to display what happens with group dynamics over time and due to things that happens. Using it as a meter of the group dynamics more than what happens to the group. Its not necessary the tension would rise because the group find themselves in a pinch, that actually could lower the tension.
When the tension rises the group sufffers together because tension creats mistrus and cooperation will be harder, maybe as someone said, slots will be unavailable on the party sheet. The effect is continuing until they adress the issue in some way and would accumulate if they get more out of hand so I think things could happen at step seven and nine. On the other hand if they manage to lower the tension the bad effect would go away.
For example, if the tension rises and the dwarf says to the elf "Its not our fault our races distrusts each other, I want to be your friend and work together with you" just to seemingly create less tension. If that happened it would be so out of caracter for a dwarf that all the other members would distrust the dwarf and the tension would rise further.
On the other hand, if the group dynamics evolve in some way and not necessarily people getting along better, the tension would lower and at step three and one beneficiary things could happen. Maybe adding another slot or some action that would be available to the whole group or recharges of actions would be faster.
Like in the last example, the dwarf and elf would set aside their distrust when they get in a really bad fight and protects each other because they know the whole group would probably die if they dont work together the tension would actually lower and some promotion might be available. Then after the battle and if they survive, the tension wouldnt necessarily rise because the group would know that in a pinch, they can trust that everyone would do their best to protect each other.
I think this way it would be an actual meter of the group dynamics instead of a ladder to climb. Both good and bad things could happen like for real but it would be more likely it would lower over time and more good would come out of it. Realisticly maybe the equilibrium over time would hover around three and with that "reward" in effect more time than not,
Just an idea