First of all I'm going to say sorry OP but I don't know how to help really, I'm not doing that great in 25 markers either -- but it isn't due to lack of content knowledge, just evaluation skills as well. I have noticed a few things that I'd like to point out though.
Currently I am taking AQA Philosophy as well, and I can also say that the OCR specification will be entirely different as technically AQA's 'pure' philosophy A level is a different subject to Religious Studies (OCR, Eduqas, etc). I understand the confusion though because a lot of schools advertise RS as 'Philosophy and Ethics' or some variation of that.
Instead of 3 papers with Philosophy of Religion, Ethics, and a religion of choice, we do 2 papers with a total of 4 main modules: Epistemology and Moral Philosophy (paper 1) and Metaphysics of God and Metaphysics of Mind (paper 2). Even if there are similarities in content, they are pretty much two completely different subjects in terms of answering questions.
I have had a bunch of different teachers marking my essays (long story), but what I can say is that the teachers used to marking for AQA Philosophy will mark the same essay drastically lower than the one with a background of teaching RS, the same essay's marks ranging from 11. The impression I'm getting is that Philosophy examiners firstly expect a lot less content and a lot more evaluation as you can see in the difference between mark distributions. Second is the hard bit: they understand evaluation in -- from what can tell -- a more complex way. This is probably why a lot of schools offer RS but not Philosophy - it's a lot harder to score the same (relative) number of evaluation marks.
This is where it becomes a bit of guesswork for me. What I think needs to be done is you need to be very specific in how the argument works and how their various objections function, and you have to judge how important the argument is, as well as making sure your opinion is around throughout and not just at the end. As one of my old teachers put it, it seems that it isn't enough to say 'Kant says x', you need to go 'This is my argument, and I will use Kant to support it'. However, I haven't really had the chance to have my essays marked by a (reliable) teacher since... probably last August.