And the size for each of these steps is at least enough so that the
big toe is placed alongside the heel.
I have noticed that in the vast majority of shuls there is not sufficient space in the pews to take three steps back with the measurements described. What should one do if he finds himself in such a pew? I can think of three possible options but do not have sources to support option 2 or 3.
Step out to a space where there is sufficient room
Take steps directly back with smaller measurements
Take steps on a diagonal so that the measurements are correct