Probably just a different mold.

I can't see rounded vs angled edging making a ****s lick of difference on a manifold style like that anyways. I ran no insert in my GT, a DIY HV3, and the L26 HV3 in my L26 UIM setup.

I noticed no difference between the DIY to the ZZP version...and I honestly noticed only a smidge better top end by putting the insert in there vs. not even running one.