I've been following this guide from Family Handyman on installing a fiberglass tub surround, and am to the point where I need to tile over the nailing flange. They say to put 1/4" tile backer over the flange to bring it out to the same depth as the 1/2" green board, as shown in this picture:
However I had to shim behind the surround, so the difference in depth between the green board and the flange varies from almost nothing to a little more than 1/4", which you might be able to discern in the below pictures:
How do I fill the uneven gaps in depth between the flange and the green board? The 1/4" tile backer can fill the bigger gaps, but I'm not sure about the smaller ones.
Do you see anything else wrong with what I'm doing?