hobless shower screen waterproofing

If someone has installed the wrong size after proper instruction they should fix it, not do a bodgie job.

This sounds like a bodgie solution. If the shower is on an upper or suspended floor, the full floor should be waterproofed anyway.

A slightly better bodgie fix might be to drill holes through the existing angle to provide proper drainage.
Install a second angle and fill the gap between them with screed or Hebel stone.
Then waterproof the addition and tile to the required size.

If I ever installed the wrong size angle and it got tiled before anyone realised it was not correct, I would be expect my builder to request it be replaced at my cost, and though this has never happened I would be happy to do so at my expense including the cost of re tiling.

Good luck and fair winds.