76x25mm stroke, 7.3x3.8 port. 787/805 with 8.4s / 7.9s, so a tad slammy

I could reduce piston weight, or spring preload, but I had another *identical comp tube but with a 3.5mm port, so tried that....
Same powerplant in the 3.5 ported comp tube gives 773/791

Both are exactly 14 fps down (I didn't fiddle the numbers, honest) - I would have expected the differential between the two to favour the lighter pellets, but it seems to have taken power equally from both ?

Any ideas on why ?

Cheers, JB

* As the tubes are different even though the piston fit felt the same, there could obviosly be some differences in power/frinction.sealing, but it's the differential between the 8.4s and 7.9s that I'm interested in...