Getting Upstands Right In Alcove

[gmt1981]

Thanks again for all the replies.

As you can see from the photograph below, I've cut away a slim section of the backerboard to allow the tray to be recessed into the rear and left sections of the backerboard.

Before i fix the tray in place and attempt to sort the solid wall on the right, does the upstand need to be flush with the outside edge of the backerboard? As it is, the edge of the board overhangs the upstand by ca.3-4mm, which would cause a void behind the tiles.

I can bring the tray out a bit so that it would be flush, but this would require me to build out the studs with a thin piece of wood which is just added hassle.

Also, what is the best way to fix the tray? Getting to the rear and central legs are a no no, and even driving a screw into the front legs looks very tricky.
Many thanks

 

[p4ulo]

It shouldn't matter that its set into the wall further than the board, the tile will be stuck to both surfaces, when you put your adhesive on (either wall or back-buttering) make sure you bring it flush then.
As for fixing, I presume the legs will be solid etc, fairly sure a plumber / installer would smear a tube of silicone over all sides that make contact and push it firmly into place. Once sealant goes off, its deffo in there.
Other option if legs have screw holes - I've got a nifty 90 degree screw-driving attachment for my driver which would be perfect?