Loop Lines?

The left side of the pump has a pump loop coming off of it and back to the intake side. It uses a jet can with a screw in jet. I use it to keep the main jet in a manageable range when we make big altitude changes. There are no lines going back to the tank. I run a racepak pro IA and havent seen any fuel pump pressure differences in plumbing it this way over returning lines back to the tank. More importantly the dragstrip dyno didn't show any differences. I suppose a guy could add enough instrumentation to choke a horse to verify all this but the time slips are a easier way and a whole lot funner.
Dave Germain