(2)450 DP's vs (2)750 DP's

I believe that this is the area where the transition is tapering off and the mains coming in. This last change of bleeds seems to maybe have broadened that area. I may just go back to the previous tune and retest.
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.