As a general rule of thumb, many springers do seem to give higher energy output figures with lighter pellets. But it is very much a generalisation and demonstrates the need to chrono with as many different pellets as possible.
Pellet fit can be / is just as important to energy and firing manners.
A further example, my old Supersport in .22. Rebuilt with standard spring and it gave 14.5 with Superdomes!
Shortened the spring and it gave 10.5. JSB Jumbo RS then gave 11.8. And RWS Hobbies, although extremely tight a nudge more. So it needs to come down again and the spring's out and lined up for further reduction on Sunday.
Piston weight, preload, spring force all important factors too.