I'm 6-3, 357 (4 XLT shirts, 50-inch waist on my jeans) and I did not fit once I got to the actual ride. it was not a problem with my calves; it was my gut, and they couldn't get the back to click in. We didn't try for long -- maybe a minute or less, and if there were tips that might have helped, the CM didn't offer them.
CMs were very nice, replaced my FP, did not embarrass me in front of my kids or other guests, but the bottom line was I did not fit. So if you are close to my size, be forewarned.