Risky
Sassy Giraffe
YES. My general rule for length is as long as I can work with it, I'll be happy. I don't care if it's a one-liner or ten paragraphs, if it's a bunch of unnecessary nonsense, then I'm going to burn out quickly.
And at least (near) one-liner responses tend to be posted much faster, no? It always helps to build momentum.
On a semi-related note, too much background information can also be overwhelming. If I get to learn your character's entire tragic backstory in your opening post, then what's left for me to discover? Well, there'd still be something, I reckon, but it sure puts out a lot of the fire.