you are probably looking at the commands for the old terrain system.
You should use advanced terrain instead.
you will find an example with media here:
http://forum.thegamecreators.com/?m=forum_view&t=97644&b=1
In advanced terrain scaling works like this:
set terrain scale terrain_number,xscale,heightscale,zscale
Supposing you have a 256x256 wide heightmap:
scale 1 will give you a 256x256 DBP units terrain (x,z)
scale 10 will give you a 2560x2560 DBP units terrain
scale 100 will give you a 25600x25600 DBP units terrain
etc..