One of our I20s had two footstraps on the rear of the boat - I've never felt so vulnerable than the 15 seconds I tried to sail with both feet in those straps...that was a train wreck in wait.
Most of the I/N 20 guys I knew ,including me , used 2 footstraps behind the beam for weight adjustment,i.e. your back foot was in one or the other depending on how bow down you were, not for both feet. I would expect that felt pretty off balance.