Please Help. (Question on fit of diapers)

I am a larger guy and I have a bit of a tummy due to surgery weight I gained a few months ago. When putting on my diaper (I usually wear abenas) The diaper usually comes up to my belly button or so (and the same height on my back) and then I tape it up. This is all fine and dandy when laying down but when I stand up the front rolls down to my waist line where my pants ride. This makes it slightly uncomfortable and makes the diaper sag considerably. Does anyone have any suggestions. As I am trying to become more active in diapers and return to being fit like I was a few months ago? Any help would be amazing!

I've had a few issues with a diaper feeling nice and tight while lying down, but once I get up and move around, it feels loose and doesn't sot on my body the way I want it to.
The way I fixed this, after taping it lying down, is either standing and leaning on a wall to retape it, or sitting in a stool upright, as if I were standing. This, of course, is limited to refastenable diapers, but I have put an abena on either standing or sitting upright to great success, and even I'm starting to get a winter hibernation gut.