A few years ago Joe Maffei was teaching a reverse grip draw from the same side ankle from the guard as part of his ground program for LE that he was working with, Ralph Mroz had the video up on a few sites, but now I'm having trouble finding it.
The book answer for ankle carry is opposite ankle, butt to the rear (right handed shooter carry on left ankle, etc.). From the position one can easily get a rather quick draw from the ankle rig to the strong hand, this also works from seated, supine, etc. Specifically from an entangled ground position I think the reverse grip thing Maffei cam up with works better, or drawing from a cargo pocket holster down on the thigh.
I went with leaving my ankle BUG on my left ankle, and adding a TDI knife concealed in my right cargo pocket for weak hand use in a ground entangled fight.