I wouldn't trust that you can be certain you're truly on the base circle of both lobes at the same time.
Do one valve at a time.

Exhaust starts to open...... adjust intake.

Intake opens and goes thru most of its cycle, then is almost closed..... Adjust exhaust.


The only way I can see 2.5 turns out of adjustment not pointing to a real problem is if it was adjusted that far off in the first place.

One tell tale sign would be if that adjuster screw is now 2.5 turns different than the others.
If it is, you have a problem.
If it isn't, it was probably set incorrectly previously.