Fat rolls (insufficient tension inside the camera) generally have leaks near the end of the roll, consisting of light coming in from both edges intermittently. Stand development itself can sometimes increase fog (especially since Rodinal varients, often used for this, aren't particularly low fog developers). I have done things like cut a 120 roll down to 127 in full room light, and after respooling in the dark, found only a tiny line of fogging along the cut -- confirming my experience that light doesn't penetrate much even in a fat roll as long as the paper is fully inside the spool flanges.
Giving the film more exposure (commonly recommended for Fomapan 400 anyway) won't help the fogged rebates, but will allow developing less, which will make the fog less dense (to be clear, its reducing development that helps here, not directly the increased exposure).
Given other reports here, it's possible Foma produced a batch of 120 that had a little higher than normal base + fog density. Developing cold (for Rodinal, you can go at least as low as 15 C, compensating time for the lower temperature by adding 7% for each degree C below 20) can help, more so if you can add a little benzotriazole to the working solution.
I opted to throw my remaining rolls out.
I would suggest, for the future, that if you have film you don't want (even if you consider it defective) post in the Classifieds here (with clear disclosure of what you believe is wrong with it) so someone else can offer to pay shipping and a little for your packaging time to receive it. I like Fomapan a lot, both the 100 and 400 in 35 mm, 120, and 4x5, and would happily pay the USPS rate to have it to shoot and process vs. going to the landfill.