Att "silent c". ardex lq 92 info

G'day, I've been reading this thread & others hoping that a solution to my problem would appear, you may have solved it for me. I have a elevated cantilevered balcony with 19mm ac sheeting over timber joists.It is about 9metres wide and 3metres deep. There is a slight movement in floor when walking on it so I have been hesitant about tiling for fear of cracking, We have a pvc liner type water proof membrane layed down without fall, would the product you suggested 'ardex lq 92 ' be suitable over this and make a fall of about 20mm down to 5mm instead of a thicker sand & cement bed( wooried about weight) and then tile over this with a flexible tile glue and use flexible grout. Your response would be appreciated( or if anyone else has thoughts)