I had the same problem with my 4.8's. I'm the same height as you and wear 34" pads but my knee kept slipping over the knee stack. When I adjusted the knee lock higher it just slipped underneath the knee stack. I'm considering moving up to a 35 or 36" pad though.
I have knee pads now though since my knees kept getting bruised and wasn't healing as fast as they were initially
. You can get some decent itech knee pads for about 30-ish I think that will do the trick.