I had seen this guide previously and have been meaning to come back and correct something:
There are certain leves which grant extensions, automatically, regardless of turning in HQ items. Generally speaking, any leve 20 or higher that requires you to turn in:
3 of an item that synths one at a time (iron spear for example)
5 of an item that synths three at a time (potions)
5 of a basic material that synths one at a time (ingots)
(You could also look at it as 3 of items that don't stack, or 5 of items that do stack).
These leves will give you the option of an extension with or without HQ items. Also, for items that don't stack, if you turn in some normal and some HQ, you will get a portion of the 200% bonus (1 HQ, 2 normal gets you 66%, 2 HQ 1 normal gets 133%)
I know there are two exceptions to the rules above for triples:
Rolanberry Cheese (synths 3, turn in is 5, does not allow extensions).
I don't remember the second, but I think it was cooking and required 9 of something that synths 6 at a time.
There's also cornmeal: synths 4, turn in is 6, allows extension.
