Does the medic promotion stack?

The medic promotion for land units increases the heal rate of that unit, and those in adjacent hexes.

I've just had a thought, but unfortunately am not at home to check, so thought I'd ask before I forget about it: Does the effect of the promotion stack?
If I have three injured units with the promotion and place them in a triangle formation (so they are each adjacent to the other two), and fortify them all to heal, will they each receive a bonus of:

• +3 (+1 from themselves and +1 from each of the other 2 units)
• +2 (+1 from themselves and +1 from a non-stacking adjacent effect)
• +1 (+1 from themselves; no stacking at all)
• Something else?

Yes, it does stack. I played a game where I had multiple knights which were all leveled up with both March (heal every turn) and Medic (+1 heal to unit and adjacent). When they ended the turn surrounding each other, they'd be able to get more than +2 (depending on how many Medic units were next to them).

I know they stack for sure, but I think it's +3 max. I'm not 100% sure of that, but I believe I had 4 adjacent medic units and they only headed +3 each turn.