Andy's right on with that assessment, I hadn't thought of that.
Though of course, if you have a 5lb plate or a few ankle weights to hang off the horns, those are very good for bridging the gap between bell sizes.
Sam, I have no doubt that more volume will probably be better for pressing. Something you could also do, if you were inclined to stick with the singles, would be keeping that 'static' volume of 63 reps/week and introducing TGUs, push press, overhead carry, floor press etc. with the next bell size up. That way, the singles for pressing would provide a baseline of moderate volume practice, and you could add heavier, more varied work on top of that.
And thanks! I've been busy but will try to post more regularly when I have the time.