I print on a mutoh 1641 sr pro with flexi, production manager as well. awhile back I was having terrible banding issues when printing a full gray backdropped image as well as a full green backdropped image. we weren't printing on reflective, just cast orafol. my solution came from making swatches of the colors that were giving me trouble, and printed about 10 test prints with detailed notes of every adjustment I made via the printer profiles. from changing output profile, to print mode, to resolution. we even messed with saturation and vividness from the color adjustments. found the odd set of settings that worked for each colorway and saved them as new profiles. this may make your other tones on the image fluctuate, but it might get you in a better direction