Apply it to the wall with the bottom edge about 1 4 in.
Transition from wall tile to bathtub lip.
The tub is designed to sit on the floor and be screwed to the studs kohler recommends setting in mortar which i did.
Similar to the gap that can exist between your wall tile and tub you may have a space between the floor and your bathtub.
This issue is sitting there for a long time now and really bother me.
Above the lip of the tub.
This kohler acrylic tub is thick the flange is more than a 1 2 thick if you run the cement board over the flange and the tile which is about 1 2 thick when thinsetted it will come too far into the tub.
I checked the tile grout.
Was the shower water seeped to the lip area from the bottom caulk and then travelled laterally out and wet the dry wall adjacent to the tub.
The best approach when installing cement board or other tile backer around a tub is to keep the cement board out of the lip area.
This video will show you how to set tile around a tub.
As with any other gap near your bathtub you ll want to close the opening to prevent any possible water damage or the onset of mold and mildew.