I find that this pass works well if the guy at the bottom does not grab and pull your heal with the ridge of his hand flush with the mat (instead of grabbing higher) this makes it impossible for the person on top to bring their knee outward.  This detail with the bottom person grabbing and pulling the very bottom part of the heal outward makes all the difference, coupled with the bottom guy pushing/kicking out the opposite knee this further exasperates the angle (the top guy is forced to turn away or fall) and requires a different approach to defend against the single leg and/or omoplata if the bottom guy quickly switches to a cross grab, the triangle is right there as well as several sweep variants and/or back taking maneuvers.   I am still searching for the best top solution to pass this variant of the de la Riva guard which I encounter frequently.  Typically I get low leaving no space between my butt and heal, putting a lot of weight on my toes, a wide base with low collar control on the same side my heal is being controlled, hiding my elbow inside my knee and a wide base with my other leg, I look for an opening on one side of the other (such as a cross knee variant with a step-over and arm control on the same side), transitioning quickly can open things up for a pass, half guard or an ankle lock.  This is a very dynamic position top and bottom.  I would very much enjoy some feedback and/or different ideas on how to overcome this very effective guard variant of the de la Riva guard.      

Humbly, Chris Malterre.