Thanks OP, just purchased to replace my Mira Sport
You are correct. 10mm would be required for a 10.8kw shower. My calculations were based on a 9.5kw.
Same with mine, cold pressure good but as you turn up the heat it plummets, have a pump driven mains shower in other bathroom thats great, shower screen dropped to bits last week hence using other bathroom and shower. Guess just need to pull my finger out and fix it
I have the 12KW Mira sport and the pressure isn't great when making hot water. Plumber recommend it though. Mine has been in 3 years. Makes good pressure when putting out tepid/cold water though.
aha that's why your called smartguy1 8)