Butterfly stretch - Why is one knee not on the floor?

Hi,
When I do butterfly stretch, my left knee is comfortably on the floor, completely flat. But my right knee is off the ground by about 4 inches.

Which muscle do I need to target to get it to stay down? My left knee doesnt even need any pressure applied to get it down, it just flops down and sits completely comfortable and flat.

Please help

Hi loosehips
R u yoga newbie ? As im still considered myself as newbie too, at first my both knee can't touch the ground too when doing this pose, about few inches to reach floor but after regular practice, now both can reach floor.
I believe if you having more practice, your right knee can reach it later too.

think what might be causing the asymmetry and perhaps address that. Do you sit with your legs crossed one direction all the time, or even in yoga tend to sit in cross legged positions favoring one side?

Focus on hip opening postures. This imbalance of glutes will be resolved with practice.