What kind of segments are you talking about?
All default wall, room and corridor segments are based on a single tile size (cube). Prefabs themselves are made up from these.
Breaking the rules and trying to scale the default segments up - over and above the standard tile size via their script could have unpredictable results.
If you want a particular size or shape object - even wall like objects and dont want to place one above the other in cases where they could be one and a half tiles high say, then make entities for them. Thus far as I am aware in my experience entities can be of any size without resulting in any unusual behavioural charateristics.
