Most 'humans' in Darklands are around 30mm to the eye. We take the view that a 30mm to the eye mini is a six-foot strapping bloke.
Eirik is a big lad (though just tall, not super-human build) - Some characters are tall and of massive proportions, like Carrowek - though he's your final act bad guy in a barbarian movie sort and is one of the Horned God's chosen- same for Kraan who has the blessing of Baalor. Carrowek will make a regular building look odd - he makes regular guys look odd!
The Duguth are unaltered men. Just regular guys - some are smaller than 30mm to the eye some are 30mm (some are crouched slightly, some stood straight) . Same with the Drune Archers- Drune Ax are bulkier than a regular Joe but not much taller. These are your more regular guys (though if a six-pack like Arthyren's is regular I want mine!)
So human terrain will be made on the basis that your average Joe is 30mm to the eye. I know 6 foot is above average now, never mind back then, but these are warriors (and six foot could just as easily be 5'8" if you prefer, it barely matters, we just like the idea of some six-footers getting stuck in. Ahem)! Terrain will be race-specific of course - not much point having Gorgonares terrain based on a 30mm doorway (most doors were smaller than the person using them mind) . Mind you as snake-men- they'd slip through nicely!