what my sensei told me because my BJJ partner is bigger then me (30 pounds) so triangle's are hard on my legs, i guess its the same probleme as you. what i do with my legs is that you take the shoulder out of the equation. Example, if you throw your right legs up onto the back of his head pull it towards yourself before you hook it in. dont try to get Head/arm/shoulder in between your legs, since you got smaller legs, just get Head/arm.
hope that helps you out.