Something like this:
on average, you can push press 10-15% more than what you OHP, this is what I've read everywhere and so far is pretty much in line with my own experience.
Say, for easy math, that your 1RM OHP is 100lbs. A fairly challenging weight for 10 reps would be, I don't know, 70-75% of your RM? Let's say 70lbs, for the sake of it.
This means that a fairly challenging weight in that rep range, for the Push Press, would be of about 77-80lbs give or take.
This is, IF you want to Push Press in the 10-reps range, which was the point of the previous posts. I honestly do not know if it's beneficial and how much.
For mechanical dropsets, it would be a non-issue: you pick your OHP fairly challenging weight (70lbs) and switch to Push Press either when you fatigue or after a certain number of reps, each set.
Regardless of when you switch to PP, the cumulated fatigue of previous reps will make PP harder even if the weight is relatively low compared to the amount of weight you'd use in that rep range with the PP.
Otherwise, I'd stick to the original math: take your OHP 1RM, add 10-15%, and program it from there using the numbers by CT's program that were listed above. Or the usual percentages (like 90% for 3 reps sets, 80-85 for 5 reps and so on).
I'd start with an extra 10% of the OHP 1RM, btw. PP is not very technical but it takes some practice and timing to get the most out of the leg drive, you gotta synchronize your body, i'm still struggling with that part.