It could be that he just has a large head, even without the fro. Wigs are not one size fits all. Most brands are fine if you have a smaller head or an average-sized head with short and/or thin hair, but people with big heads and/or thick, long hair won't fit in them.
Check out Arda Wigs with your boyfriend. Their wigs are sized larger to accommodate bigger heads and lots of hair.
FF9 cosplay? Hit me up!
I now have a Tumblr
. Sometimes I use it.