This raises a question. When you say passes are you talking one round trip on the strop or one pass is going up and another is going down?
Sorry, I probably expressed myself wrong. What I meant are "laps". That is once up and down on the strop. So do 20 - 30 times up and down. I believe 20 on linen and another 50 on leather is just too much. You dull the razor prematurely doing that.