The ring lands on a KDX piston are supposed to be the same size.
BUT, you will likely find that the rings don't think so!!
When putting the rings on the piston, each ring must be free to move in the land. Any bind or catch is not satisfactory.
IF you find a ring is snug in the land, try the other ring in that land. Likely the snug will be gone.
It's a good idea to dress the end of the rings, too. The cut in the ring to fit the pin can leave a snag that will hang up in the land. A couple of strokes with some backed/supported (sanding block) wet-n-dry in the 400 grit range will clean 'em right up.
Uh..dress the rings from OUTside to INside.
Ring pliers sure are handy.....
Oh...mark on the rings goes UP!
Cheers!