I don't want to upset you Sandman mate, but I do disagree slightly.
A friend of mine is currently breeding some dutch rams (i dont know if these are smaller than the german ones) in a 2'x1'x1' tank which has about 10 gallons after substrate and rocks etc, the have not bred yet but are very happy and do not squabble at all, they've been there for several weeks now and although still a bit juvenile, seems they may start breeding at some point.
Tanks mates are a few guppys, exellent tankmates for them as they continually produce fry which the Rams hunt for, so getting them into condition is a relative doddle.
I understand that some may feel this is cruel to the guppys but it is after all a very natural part of life in the wild, and as fishkeepers it is a common goal of ours to replicate a natural enviroment and behavior for our fishes.
Obviously the tank has plenty of plants, hiding places etc so the fry do have a good chance and a fair few survive to be too big for the Rams to bother chasing.