I’m trying to test it, but it’s a bit complicated because there are many things happening at once that can affect the hunt.
From what I’m seeing, it looks like the base healing from attacking is higher, but not the healing from using spells. Your attacks seem to have more base leech, which is strange because it appears to activate only after consuming Harmony, regardless of whether you are standing on the field or not. This applies to the leech or healing from your attacks.
I’ve noticed a real increase even when I’m not standing on the field. What the field definitely affects is the healing from your spells: the 10% increase is noticeable there. I haven’t been able to confirm that same effect on attack healing, though. It also seems inconsistent; sometimes I notice more damage and other times I do not.
Damage is easier to measure by simply hunting and checking whether it is more profitable or not. What I can confirm is that you do receive more healing from attacking after consuming Harmony, whether or not you are standing on the field, and the healing is even higher when you are standing on the field.