metal shower waste installation

Hi,
I am renovating my bathroom and got stuck with floor waste.
Before I had one of those plastic wastes with flange long enough to go trough screed and sit inside the waste pipe. I am going to put metal grate instead but got stuck.

Metal wastes I could find have very short "pipe" at the back, so it won't sit in the waste pipe, leaving some of screed open to water.

I found "smart tile" waste, and its installation instructions say that it "should not rest directly on the wet seal or inhibit sub-floor moisture entering drainage pipe". The picture there explains what I am talking about - I have almost the same situation with plastic waterproof tray over concrete slab, puddle flange and cement and sand subfloor over it. I'm afraid if I install waste as shown the water will quickly ruin the screed.

So how it is supposed to be done?


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