The general rule of thumb (from the Sapien’s Instagram thread) is that the mandalas work best within your aura, which for most people can be approximated by stretching your arms out to your sides. The closer your mandala is to the center of your aura, the greater the effect the mandala would have on that person.
There’s a belief that, as the mandala grows in strength, its range grows as well, yes.
I’m not Sammy or the Cap’n. IIRC, it does. Was there a particular reason for you to think that it doesn’t contain a field? (Maybe I missed something?)