I dont know about where you train but UNDER 180 is a minority here at my 2 schools. I'm approx 165 now and I have guys from 180 up thru 260 that train with me in
primarily RG. As Coringao stated above, they can sink anything save for a few super flexi positions (Sorcerer, etc). In fact my biggest guy (Recently cut from 260 to 250) is one of the few that can hit double lotus. Size and weight can obviously be a limitation in some cases, but those are few. Anyone can become flexible and 10TH Planet Jiu Jitsu is not weight or size restrictive. The fact is our system is more allowing of open mindedness and adaptation. For example Eddie will remind you all that a simple move like the Tepee is the brainchild and adaptation of a short-legged practitioner named Scott Rodondo (MTRG pg. 159 -Tepee) So, to answer your question directly, i'd venture that the success rate is somewhere around 95% provided that person applies himself, stretches and reps his balls off! And thats no different for us smaller guys either