An 8 cm cistern is not automatically a better choice than a 12 cm system. The depth affects the carrier, pipework, flush mechanism, finished wall and available service space, but the exact product and installation type still determine what is possible.
The cistern depth is not the finished wall depth
Tiles, adhesive, board, waterproofing, plaster and the pan projection all add to the finished build-up. A thin cistern does not create an 80 mm finished wall by itself.
Check the frame and pan together
The selected pan, carrier, waste connection and flush plate must be compatible. Mixing a visible pan with the wrong concealed frame can create a costly installation problem.
Service access still matters
The flush plate opening must provide access to the internal components allowed by the system. A thinner prewall should not be achieved by sacrificing safe maintenance access.
Choose around the room
An 8 cm system may suit a constrained renovation, while a deeper 12 cm system may offer a different range of components or installation options. Compare the whole assembly: frame, cistern, panel and finished surface.
Read about why a flush plate is also a service opening, or see why the finished wall thickness matters.