Not turning to the Dark Side, are we...??!! :scratch:
The height only really depends on if you intend to a) use magnetic uncoupling, and b) what else you intend to couple to? IIRC, UK stock has higher clearance under the buffer beam than US stock, so to set Kadees at the US-spec height requires some filling in of the gap.
If, as I assume, you're thinking in terms of coaching stock, it'd be worth finding out at what height other modellers are setting their Kadees, or at least the ones you intend to run your stock with... then just be consistent in setting your kadees all at the same height.
This link:
http://www.kadee.com/html/S-G%20body%20 ... %20ins.pdf is a pdf file of the instructions for large-scale kadees; at the bottom of page two it gives the setting measurements for them; as the US still uses Imperial standards (more British than the British these days!!

) I hopr you're up on your fractions of an inch... ???
