You would use Durabase WP on the wall area the use of Durabase CI mat with concrete leans more towards preventing cracking of tiles due to screed movement on a new build.
The gradient is 2% in the top surface. The total instal height of the tilux base is around 100/110 mm depending on base used so your trap should work within your confines.
Have a look here daniel :
Youtube Tilux wet room shower base tiler
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