Back Flip
A back flip is easier than a front flip or side flip.
(cf. Back flips are easier than front flips for us )
It is because of human body structure and technique of a round off (and handspring).
Therefore, there are some people who can do full-twisting double back on concreate.
Standing Arabian front flip (back tuck with an early half twist)
Round off and Back Hand Spring makes your back flip better.