Debelius and Kuiter says 7 -12 cms, however I would bear in mind large angels are notorious for getting 'stuck' in this process. This might be a function of tank size, diet, water quality and over aggressive tankmates subduing them.
You don't have a rowdy tank, but it isn't very big and you do have some fish in there so keep an eye on water quality and really try to vary that diet,and add a lot of seaweed, and the specialist angel foods