I think you're right and that's why people use them as dithers. What about congo tetra's? Growing out 7 in a twenty gallon to put in my 210 with ca/sa cichlids. Or are they too cool for school?
Goliath tigerfish. You could keep 6-8 for life in a 20gal.
KIDDING
I like the Congo tetras. I would imagine you could do three in a 20 gallon, a male and two females. You might be better doing assorted little ones, like golden tetras or cardinals. I love the look of multiple little chunks of gold and silver swimming around