Hi, I'd really appreciate a bit of advice with the following, if you can understand what I'm going on about!

I will be tiling a 1500x900mm Impey Aquadec with offset drain which is fitted into a recess of the same size. I plan to envelope cut 40x40 limestone tiles to fit the former.

My main concern is that the Dec has a fairly large flat area around the edges, approx 70mm on the long edges and 35mm on the short edges. This has the effect of reducing the dec area with a gradient to nearer 1360x830mm.

Obviously I don't want a strip of level tiles around the edge. Would I be ok to do my envelope cuts from the corners of the square gulley to the very corners of the former, effectively building up the gradient on the flat area of the former with the adhesive? Bearing in mind that this will take my envelope cuts slightly away from where they would be if you took a line from corner of the gulley to the corner of the graded area.

Sorry to waffle on but it's quite difficult to put into words.

unfortunately you haven't got much room for manouvre with that size tile. All you can do is dry lay them and see if you can build up the outside of the former (perhaps 6mm hardie)to match the fall. (if you get what I'm talking about)