There's a lot of discussion here among different people and scenarios that I'm trying to unravel.
First question: is this a matter of the fuel trims moving around more than would be ideal or is there an actual driveability, knock, etc problem?
Second: Are we talking about stock port injectors, obviously stock DI injectors, and stock MAF scaling or scaling that has been judged ok before the PI and DI balance was changed?
I suspect there's a bunch of wall wetting compensation, gas flow model, or injector flow compensation that is poorly understood because we don't have actual block diagrams of how the software works, just whatever has been reverse engineered.
My position is, generally speaking and subject to case by case revision--if the fuel trims are just moving around more who cares? That's their job. They're compensating for some inscrutable fuel calculation that hasn't been unraveled, or more likely, production tolerances in injectors, given that the stock values were for some mean spec part most likely.
Is there an actual problem with the car here or are we just trying to make the fuel trim lines on an excel graph look pretty