Yarrow Flower + Any potion (Minor or Medium) will result in a healing Elixir, so go with minor one instead.
And Minor + Minor works. However, there are some iffy cases where It says "Minor Potion" on the name and icon but if you look at the effect properly, it's a poison potion. Check if that's the case because when you have multiple stack of minor potion, one of them is the poison bottle.
