[pmrid (Peter)]

I've just bought a Hotech Field Flattener for my ED127 refractor. I am wondering whether there is any specified or optimal distance/separation that should be maintained between the flattener and the imaging chip. I recall, for example, that the Baadr MPCC required a very precise 55 mm separation but I haven't been able, so far, to discover if a similar thing applies to these Hotech devices.
Anyone know?

Peter.