gain interferes with BB. at what point is dependent on both BB and gain settings. I remember mr. G. somehwre showing a way to make gain not interfere with BB (or to a lesser extent), sadly don't remember how it was set.
I take this as a safety feature. If the Bollinger bands come close, which happens, gain setting will assure you don't loose money.
At least I see it this way. Mr. G. builds a lot of safety features into the bot as to make sure beginers don't start with loosing money. Loosing money comes later, with more experience ...