The world may never know lol.
Actually we have been working on finding my girlfriend's after I found it by complete accident. We just try different positions, angles and depths.
The best position we found was she is laying flat on her stomach and I enter her with more of a downward thrust instead of straight in, adjustments might need to be made for this position depending on how much junk is in you trunk and my girl has quite a bit.
Its pretty much a lot of guess work, feeling around, and communication. He needs to start in a position and you need to kind of guide him by telling him when he is close, what position is working best, and what he was doing. Just try and do better then saying "you were reeeeeeeeally close" or " not quite" cause those don't tell us guys very much.