I think the tiles will most probably end up fairly level with the mat, with a 9mm tile plus adhesive, depending on how flat the floor is finished height would be around 12-15mm. I'd use a 10mm trim and some small plastic wedges to keep it tight to the tile. Might be worth going for a stainless steel trim as the aluminium ones only have a anodised coating that would wear off over time with foot traffic. The last mat well I tiled never had any trim (the customer's choice) but used the finished edge of the porcelain tile.
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