F Series FX Loop Mod Question

I recently purchased an F-50 head. I absolutely love it. First Mesa, so I found the EQing a bit awkward, but I do love it

I modded the FX loop so that it can switch between parallel and series. It works completely fine (I think), but I notice that my effects, such as reverb, sound way more “stronger” in parallel than series. Is there an explanation to that? I would have thought it would have been the opposite