I've always wondered why my syn seemed so small to you...not that it upset me, just gave me cause to wonder...
That particular male was a good 7inches when he sired this spawn. Just 2 inches less than your male is
now. I personally don't see that as such a significant size difference, especially considering your male probably wasn't 9 inches 6 months ago? It's sort of a moot point anyway, I sold that male as part of a purebred pair. I do still have two pure syn males, siblings to the father of the fry.
This ones my favorite, he's 8+ inches & head starting to pop slightly...take note of exactly how tall bodied & thick this fish is, 8 inches long and probably darn near four inches belly to back. One of the uncles (pictured here with the mother) to the fry from this thread...

...although it's a brother to the one pictured, the other male hasn't always been mine & I fear it's been heavily stunted. I don't have a pic of him yet, Id like to pump him up for awhile before I show him off...
He may never reach even average size for a male syn, I hope I'm not too late, but he's awful small for his age.