I am building a new home. The drywallers installed Durock on the
shower walls. However, there is a raised threshold (3-2x4s) of 4-1/2"
at the entrance to the shower. The Durock sheets stop at the threshold
height, 4-1/2" above the shower pan. I have now installed a mud bed
that is 2" thick at the shower edge. So, there is now a space of
2-1/2" from the top of the mud pan to the beginning of the Durock (the
shower pan material goes up the wall some 9" or so.)

My question is:

Do I fill in this 2-1/2" gap with a strip of Durock? Am I concerned
about water wicking up the Durock?

Or, do I just allow the tile on the wall of the shower to overhang
this "empty" space, perhaps filling the void behind the tile with
extra thinset?

Thanks for your help.

gary comfort
Ponce Inlet, FL