No, you are wrong. Power level doesn't alter Psy rating for the purpose of the Focus Power roll, you always use your base rating. Power level only applies to the final effects of the power.
And here we go again…
This Response from Tim should put this issue to bed:
"You do, in fact, add the +15 Bonus to the Focus Power Test.
Thank you for your question,
On Feb 1, 2012, at 3:58 PM,
This question concerns psykers, psy rating, and pushing.
Psykers may add a bonus to their Focus Power Test equal to 5 per PR used for the power.
When you push a power the rules state (pg. 185) a psyker, "may add +3 to his Psy Rating when determining the power's final effects" [sic].
This appears to indicate the +3 only affects the final effects, i.e. damage, range, etc. of the power but does NOT give an additional +15 bonus (5 X 3) to the focus power test to manifest.
Is this the case or does the +3 also contribute to the bonus to focus power tests?"
According to this answer the Psy Rating used in manifesting a power does translate to a bonus to the focus power test.
Yes Psykers are powerful in Deathwatch.
Yes, it would be nice if they were reworked a litte.
But, I've yet to come up with any method to do it right myself.
So, we'll either have to suffer the status quo, or hope FFG fixes it sometime.