Should not be a problem with your set-up. I p[lace my tanks on the balance point. The balance point on my Q racers is 3" back from the L.E.

Some ideas.

Is the pressure line nipple hole at the engine end big enough or possibly blocked?

Is the tank truly airtight and not leaking any air?

The fuel pickup in the bag should go just half way into the tank, not all the way to the rear.

There is a possibility that the bag blocks the end of the pick-up. I cut a vee into the end of the pickup to prevent this. I also pierce a small hole across the pick-up line 1/2" or so up from the vee. I use a small prass tube to pierce the hole.

Could it be a radio problem and the engine is idling down?

That is it, I cannot think of anything else.

Ed S