That could be the design.

At one time, I felt my strop was buckling ever so slightly in the middle not matter how taut I made it. I would strop and thought the middle of the straight razor was always a little sharper than the toe or heal.

I used my pasted paddle strop to give about 10 strokes to the toe and heel, then used a 20 x patterns to keep it all even. After this effort, my entire straight was equally sharp and I have since reestablished a flat strop from end to end.

The best investment I made in strops was my trusty 4 sided pasted paddle strop from Tony Miller. It always comes in handy in maintaining my straight razors.

Pabster