I agree with Slappy*McFish. I added 3 clown loaches about 2 weeks prior to the RTS. They were all about the same size (under 2 inches - I couldn't find them any larger). Sadly, 2 of the loaches didn't make it. In the following weeks, the loach has grown with the RTS and is clearly more dominant. The loach and the RTS are inseparable, though I know it's because he's looking for a companion.
I need to find several larger loaches but in the meantime, they get along fine. It's been about 3 months and the RTS is approx. 4" while the loach is just under 3.