A plausible theory. I had also considered that it might be a deliberate limiting factor, to prevent me from healing a large number of people at once. The amount of healing seems relative to the amount of liquid consumed, so splitting a single serving between multiple people would result in partial recovery at best.

But, it's more mundane uses can't be denied. If not for the delivery method of the healing, I would be deprived of my usual cafe order. And it's saved me a noticeable amount of money, as well.