It will sometimes depend on the CM. We've been on the AquaDuck dozens of times where first I'm in front and DH is in the back, then we switch and we switch back and forth every ride. Last time the CM said that the heavier person HAD to be in the back and wouldn't let us switch. Some CMs are just naturally more cautious than others and/or more strict with the rules. So some CMs might allow wrist mount but don't assume that they all will.