Well, let's backup! While Hardieback is a good choice for walls, it serves no purpose under the mudbed or on the curb. There must be a preslope under the liner so that the liner is sloped to the drain. The drain should have weepholes that you must ensure remain clear when the setting layer is installed. Depending on what's underneath the drain (wooden subfloor or a slab) would determine how thick the mortar needs to be at the low end (it can be thinner over a slab). There are all sorts of ways to make a proper shower, but it is all in the details...doesn't sound like you're getting started correctly. Suggest you check out www.johnbridge.com and look in their 'Liberry' for some guidelines, then ask your questions there. Personally, I prefer a surface membrane verses a conventional shower. My shower of choice is made by www.schluter.com and is made with Kerdi, but there are other methods that work.