Covent wrote:
While improved natural attack is a virtual size increase, Beastial aspect is not as it never makes any mention of size or size increases. They should stack with each other and enlarge person.
Your GM appears to be incorrect.
Thank you for the clarity of your question and the links.
edit: or just re read the FAQ. I am incorrect, your GM is correct my apologies.
Wouldn't BA and INA count as effective size increases?
"The same is true of effective size increases (which includes “deal damage as if they were one size category larger than they actually are,” “your damage die type increases by one step,” and similar language). They don’t stack with each other, just take the biggest one. "