I've just checked my own 1861 over 1 and, surprise surprise, it also has an open P, although I can't make my mind up whether it's exactly the same font as seen on my F20 and the F36 and 37 proofs.
F33 1 over 1, F36, F37, F20 - it's the foot of the P that is clearly indented on the right hand 3 coins but I'm not sure about the F33.
Interestingly, the F36 also has a 1 over 1 although the date is wider: