Something else to consider with injection molded parts - drafting.
Squared corners are often not square, depending on how the kit is designed and engineered. A perfectly square corner is very difficult to remove from a mold, so most “square” corners are at a slightly obtuse angle.
Correcting these won’t necessarily help with fitting issues, and could in fact make them worse, because two adjacent parts with off angles are designed to fit together to from a correct angle.
This thread showed not just some very bad molding on the P-40 kit, but further down shows extreme cases of drafting that are very readily apparent: