My wife and I have tried several time.
In fact, just last Saturday. She was sitting on a long black dick. When she orgasimed, she collapsed forward onto his chest and I was like... let's try again.
Lube up, wiggle my knees between his legs and hers.... pull he back to get the elevation and angle right... slip it in her ass (something I do on a weekly basis).
Now he can't move as i have her pushed down for the height I need, so he is pinned and can't move. So, I try to move her forward and back to get the motion for his dick... couple back and forth, and hes slipped out.
I pull out, she lifts up, slips him back in. I slip back in, couple pumps, and he is out again....
Maybe we're not the right hwp? Maybe the bed was too soft so my knees sank too much? Maybe I'm not long enough or maybe he wasn't rock hard enough?
Whatever the issue, once again, it just doesn't work.
If you watch the pornos, you will see that in most the bottom guy is not moving at all.
We have actually had better luck with dvp, but even that is not nearly as good in reality as fantasy. Trying to get in deep, the dicks are trying to x or v. To get parallel, you end up with just the tips in.