Mortar shower base

This is problem #2 which involves installation of a mortar shower base, my first experience with this kind of shower. My plumber who did most of the work on the house has 30 years' experience and he recommended this kind of base over Widi shower bases. We visited Home Depot where he selected Rapid Set Mortar Mix , described as a high-strength structural repair mortar. He did the first application of mortar to establish a sloped base. The mortar set up so rapidly that it took off leaving a finish that was not wonderful. After watching several YouTube videos and discussing with a friend who also does this work, I visited a pro supplier and purchased Mapei 4 to 1 Mud Bed Mix which is described as ideal for floating shower bases . All YouTube videos showed applying materials in a very dry condition; some showed using a 2 x 4 and a hammer to help consolidate it. Interestingly none of the videos showed a mix consistency you would see with regular cement products.

I didn't want to tell him how to do his job and thought perhaps he would read and follow the instructions with his 30 years' experience as I had to leave for a dental appointment. Probably he wouldn't have listened to anything I would have to say anyway because what do I know compared to him?

The product is described as 'ideal for floating shower bases (3/8" to 3")'; the instructions are in quite small print and read "Mix to a dry or semi-dry consistency that can be formed by hand into a small ball without crumbling apart". It appears there may have been twice the water the manufacturer recommends, and he treated it as a self-leveling kind of product. The result was bleed-water lasting over 4 hours which he suggested I soak up as he had to leave after I returned from teeth cleaning. After drying, the surface was very sandy, and it clearly had to be demoed which I have now done; thankfully it came out easily as it was very much like sand.

My questions are: the membrane only extends up the wall about a half an inch in one corner, would this be adequate? There's some leftover material that can perhaps be taped onto it to improve it, using blue tuck tape? The second question is should the wall panels be installed before doing the 2nd coat of product and what kind of panel material is recommended? Would blue drywall be acceptable if kept above the finished floor surface with perhaps a metal corner bead and some silicone sealant between the corner bead and the floor tile or should it be cement-board or Widi panels with Widi adhesive at the junction? Applying silicone at this location may result in ongoing maintenance/cleaning/mold issues. I already have blue drywall panels cut to fit but can perhaps find then another home or trash them. Would another thought be to use cement board or Widi panels for the first 1 or 2 feet and transition to the blue drywall with a membrane over?

I will be seeking professional help with the shower base plus the tile work for this and repairs to two other showers and would like someone who is familiar with the tile installation standard ANSI A108/A118/A136.1:2021 - Installation of Ceramic Tile . There are no standards referenced in our Building Code however anyone doing tile work commercially or for professional home builders should know of this standard which may be specified by the general contractor or registered professional. I'm also interested to hear any thoughts if there are any shortcomings in the standard which should be added to the work description for the tile installation?