Here is the latest. This might be a bit obsessive or pedantic. I have used a piece of 25mm thick aluminium as my contact surface for the base of the pier.
Rather than have the pier onto concrete which is level and flat I thought I would try to use a metal contact surface, this is far smother and flatter than the levelling compound. And if I wanted to get really pedantic I could have the surface machined.
I have used 16mm stainless steel Ramset chem studs to hold the aluminium plate down. I will then tap 16mm holes for the pier. I will anodise the aluminium to protect it from oxidisation.
I am calling it a pier to concrete interface.
Cheers
Phil