There is never a reason to cast the Heal spell at less than Force 6, unless casting recklessly or part of a Preparation. The Drain value is F-4, which is 2 if cast at Force 6. Since the minimum Drain value is 2, it's a 2 at 1, 2, 3, 4, 5, or 6.
Even though you only need to heal up to 3 Physical Boxes, additional hits beyond speed up the casting as well as cover for any oddities that make healing tougher.
So I'm going to assume that with that knowledge, you cast it at Force 6.
So, the First Aid didn't net enough hits to actually heal any damage. We'll chalk it up to the oddities of Biofeedback damage.
The Heal Spell heals up the Physical Damage fully, but Kumiho remains unconscious for the moment.