I must be doing something wrong, because basically none of the potion recipes work for me. I have empty potion bottles, and the right potions according to the list. I can combine small healing up to mediums....but I can't make larges work at all. Also can't combine any resist potions to make resist alls, using the same strength of each ingredient.
When you combine two Minor Healing Potions, the resulting potion is determined by your Crafting skill. If it is 2 you get a Medium Healing Potion. If it is 3 or more you get a Large Healing Potion.
When using potions (other than healing potions and poison flasks) as an ingredient to create another potion, only the minor variant seems to work. So to create a Minor Resist-All Potion you need to mix a Air Resistance Potion with a Water Resistance Potion or a Earth Resistance Potion with a Fire Resistance Potion. All these 4 potions must be of the minor variant with a +15% resistance bonus. Also, note that you need a Crafting skill of at least 3.
Hope this helps.