Amount for magic elixir about right (10)
I believe the answer is:
proportion
'right' is the definition.
(thesaurus)
'amount for magic elixir about' is the wordplay.
'amount' becomes 'r' (R is an example**).
'for' becomes 'pro' (I've seen this before).
'magic elixir' becomes 'potion' (I've seen this before).
'about' means one lot of letters goes inside another.
'pro'+'potion'='propotion'
'r' placed within 'propotion' is 'PROPORTION'.
(Other definitions for proportion that I've seen before include "balance" , "Part - one needs a sense of it" .)