When I try combining minor healing potions with Crafting 0 or 1, they just stack, with a 'not enough crafting' message. At crafting level 2, I consistently get medium healing potions.
Are you supposed to get the large ones from combining small potions when you have higher crafting skill then?
That's a little abstract for me

I figured the crafting skill would determine what size of potion you can combine not the result of combining the small ones.
If that is the case, then it looks like I have not been paying attention to what character was selected when doing the crafting in other inventories.
I made a video you can check out:
https://www.youtube.com/watch?v=uEcRgvyAJw8Edit:
Alright, I did a little test run:
crafting 0,1 >> small + small = 2xsmall (stacked)
crafting 2 >> small + small = 1xmedium
crafting 3,4,5 >> small + small = 1xlarge
Looks like I was wrong. I'm still unsure tough whether or not this is intended or not.
This means that combining potions with crafting 2 is terribly inefective, basically wasting 1/3 pots.
good to know in any case.