Wet-Room Tanking/full water proof

[missbuilding1978]

Hi guys,

I am in the final process of completing my wetroom prep before tiling. All that is needed is the waterproofing and my mortar bed slope to the linear drain.

I have applied waterproof backer boards, now I am ready for tanking/waterproofing.

My question is should I fully Tank my backer boards wetroom or just the corners/edges and where the seams of each board meet?

I feel that the whole room is not necessary as the board itself is a cement front, foam backer waterproof. Only the corners (in/outs) edges and seams.

Your thoughts and opinions on this, please.

Thank you.