I'm 5 ft 6 in and don't consider myself to be a tall person by any means, but I can tell you that I do have trouble with some moves, even at my height. Namely, in Flex Train the bear crawls into pushups in the warm up, then one of the first moves where you go down to the side, put your weights down and then pick the weights back up and do an over head press.
In Cardio Core Circuit the moves that I have to modify are the jump forward, squat thrust, push up, back up into jacks - I can do the jumps forward, the squat thrusts, but I can't go down into a push up that fast and come back up to do the jacks. The squat drop and rolls are hard for me to stay on Cathe's count and the final core move where you squat drop into a push up and roll back. Again, its hard for me to keep the tempo on that one.
In All Out Low Impact HIIT, I can do the squat thrust into high switch kicks, but again its hard to keep Cathe's tempo on that one
In HIIT 40/20, where you do the burpee, push up and straddle jump (I think its in that order), I can do the burpee and the straddle jump, but I can't do the push up because I can't keep the tempo otherwise.
I think mine comes from the fact that I'm not a very flexible person, plus the fact that I'm always mindful of my knees, even before my knee injury last June.