No, the radius is as the outer ring here, all the time.
Yea, what we do now is forcing people to get closer for heal, but I'm not sure it will affect good players that much, since they require less or no extra heal except for the regular food that's on the levels. I'm sure it could be a thing in bossfights, but then again, good players don't really lose that many lives out in the field so they can waste a few ones on the bosses w/o caring.
If the priest and paladin would also give out a buff then I'm sure good players would stick around too.
The only downside from healing others is if you care about score, cause 'damage' dealt as heal doesn't count in the scoring but you take time to heal instead of killing other things.