I managed to get my razor sharp enough to get decent shaves. But I noticed that stropping made it duller instead of sharper.
I analyzed what I was doing exactly, and I think I found my mistake.
I make an X motion over the strop because it is narrower than my razor.
But while I was stropping, I noticed that the light reflected differently from the places where my razor touched the sides of the strop.
During the X motion, these places would travel along the edge, so that they always stayed at the sides of the strop.
My theory is that I used a little too much pressure on the razor. Since it is a 5/8 full hollow, this caused the edge to curve / bend around the sides of the strop. As a result, the very edge of the razor got scraped against the sides of the strop, causing it get duller with each pass instead of sharper.
Does this make sense?
I rehoned my razor, and I use virtually no pressure at all on the strop.
And now I noticed that stropping makes it slightly sharper each time, since the number of places on the edge that pass the HHT increases each time.