We had a similar problem with Anvil 980 tees (which is really Gildan now): Simple, 1c print... but it was a 12"w x 1"h rectangle. Shirt aside, there's nothing worse for giving "see-saw" action & showing crookedness. But we slowed the press WAY down, loaded meticulously, and the shirts still made it it impossible to really keep it consistent. It was one of those jobs (well, 2 in a row, for the same customer) where you have no choice but to settle for "good enough." Printed a similar layout for another client on different shirts the same week & had a much easier time.
As for suggestions: if you aren't using lasers, and if the shirt color is light enough, you can print the pallets, then flash them. That will let you see exactly where the print is landing per shirt as you load.