As a test, try more main jet
It's simple to do. See how this affects the driveabilty first then look at your numbers. It seems the changes you're making are not changing the a/f ratio much in the area you notice the problem. Take a bigger swing and try to move the a/f a whole number just to see if the motor likes it. You can figure out what change you want to incorporate to get the resulting a/f ratio after you determine that is what the engine wants in the area where the problem exist.