Yes. Both long and short work. But not too far in either direction.
When we browse for additional RPs, we look about like this:
First step is an intriguing title. Hard to define what goes there, but too little or too much there is a putoff. Same goes if the title is misspelled.
Second step is first impression. If there's hardly any text, everything vague in the intro post (no matter if it is OoC or IntCk), or if the whole thing is a text wall with no spacing, then that tends to get us to go elsewhere.
Third step would be initial reading. If the intro is poorly spelled, confusing or seems to lack in spirit, then that chases away. For short ones, the whole post falls here. For longer ones, it might be that just a few paragraphs are needed to do so.
If the above three do not scare away, it will typically go into one of these two fourth phases:
If long, complete read-through to see if it is worth joining. If short, question phase. In that, we would ask questions to determine if the GM appears to have sufficient plans for RP to be likely to be viable. On longer ones, that phase might come after the fourth phase to clarify anything unclear in the full post.
A pass on all those four (or five) steps will generally mean that we try to join an RP. We have a feeling that many others use similar methods when they pick RPs. GMs might (from our guess) use similar ones to make RP attractive to players, turned about somewhat to fit for creator rather than player.