Geberit UP320 fitting advice please

Hi,

I about to start remodelling my bathroom and have a back-to-wall WC and therefore plan on boxing-in a concealed cistern. I'm not building a false wall to the ceiling, just boxing in to above the cistern install height so I'm left with a shelf of sorts about 6-8" deep.

The Geberit UP320 seems like the one to use but has a height of 1080mm which I feel is a bit high. This is from the Geberit website:
Installation height 1080 mm (can be cut down, depending on the WC pan performance)
Minimum install height 950 mm

Does anyone have much experience of these cisterns? When it states "can be cut-down" I'm guessing that it's just the flush pipe that would need cutting? Also what is meant by pan performance and how would I know if I was safe to cut it down to 950mm??

Thanks in advance.
Paul

THey do a shorter version - not as slim though.

Yeah I've considered that - I think that's the UP200. I think it's a bit too short. The toilet seat would probably clash with the flush plate on that model...