Freshly cut stems will do best if seperated and they get light right to the base, once they get established you can easily just push them towards each other using what we call affectionately... The Bulldozer Method
Works great... just put your fingers into the sub a little bit and slide the plant over substrate and all. You can easily tighten up a patch of stem plants this way. Just do it slowly and its easy.
I have moved plants 2-3" this way.