From the Kay Erdwinn’s Post Teaching Yoga for Round Bodies
Keeping the arms close to the body and the legs together are the challenges here for the fat person. I generally let my students put their arms in an abducted position like airplane wings. The legs can be strapped together — not too close; allow a few inches — or the fat student can simply do the asana with spread legs.
The danger here occurs when the legs are so wide it affects the thigh and buttock muscles protecting the lower back. I have found that most fat students prefer to do the “cross-extension” version of this asana, lifting the left hand and right leg, then vice versa. This is safer for the lower back and is easier to perform.