I went to a study day on OFP with Jean Sutton last year and she is amazing. Everything she said made so much sense. As for evidence, she has 45 years experience as a midwife and has been dealing with mammals giving birth since she was a child. She has studied the mechanics of giving birth and knows what she's talking about.
Read her books, go to a study day, then you will understand.
There's far too much to it to go into here and you need to see the diagrams to fully understand the mechanics (at least I did).
The thing is to listen to your body tho, if it is very uncomfortable in a recommended OFP position then it is the wrong position for you. Also if placenta is anterior there is little point doing OFP until about 38wks when the uterus has grown enough for the placenta to move up enough to allow baby to rotate.
The way I see it is that if you do your OFP you give yourself the best chance of an OA baby, however, you may have the 1 of the 4 kinds of pelvis which makes it easier for baby to come out face to pubes. That's just a variation of normal.
The big problem is that the maternity 'system' we have now does not allow for decent patience, support and encouragement in labour to allow an OP baby to turn. This is why we have such a shocking rate of CS for 'failure to progress', along with inductions for arbitrary dates rather than valid medical reasons.
I just don't understand why credence is not given to a woman with a lifetime's experience in helping babies to get themselves born.