PL Comp Bench - Feet Must Be Flat

Little background
I’m a raw bencher, max around 340, and I want to do a powerlifting meet, but the local one (USAPL) says that for bench, feet must be flat. I’ve never benched like this, adn when I try now, I feel comfortable flatfooted upto around 275, but after that, I look tightness and have to go back to tucking under and being on my toes. Any tips, videos to help with this transition?