Hm, after testing with a minimal modlist, the grid sizes are properly modified by the mod settings for this mod. It is likely that there is some kind of mod conflict.
As for the original issue, I do remember now, if a mod-added vehicle already has a grid, it will not be affected by the customizer mod, since it is assumed that those mods have their own grid size settings (at the very least, it is not possible for me to know if they have grid settings or not, so it is safer to not modify them in favor of their own balance)
For the Aircraft mod in specific, the only aircraft that will have its grid size affected by the values from this mod, is the Cargo Plane, because it did not have a grid to begin with. The Gunship and the other military aircraft will have their original grid sizes preserved. See previous discussion thread for additional context
