Problem using a healing spell instead of food

[atleast100 0]

When grinding a paladin character I'm having a problem with getting it to use holy light as its food option. The problem is after it's low on HP and mana, it drinks first, then once it's full mana it starts trying to cast holy light but is sitting from drinking, so it just gets an "you must be standing to do that" error over and over and remains sitting until it's at full health. This is in vanilla by the way 

Edit: I did find that I could set the health percentages to 1%-2% and get it to just heal within the fight script