Any question answered...

Are you planning to take a dump from space?

Cold fingers plus telephone posting=look like idiot

close coupled is not the same as concealed so which do you want?

Concealed I reckon, if those are the choices

What's causing the height restriction? If the cistern is being mounted inside a stud wall whats the problem? or is it going inside an existing unit?

It has to fit under the window.

The current setup is a conventional dunny and cistern, but at some point the dunny has been moved about a foot forward and an extension put into the soil and flush pipes, I presume to give the flush water more oomph to clear the pan.

It is not concealed, and very def not close coupled- distance coupled, maybe.