Inconsistent bronze values; what's correct?

I was reviewing my Spins log (under LOOT & REWARDS) and happened to notice a pretty large bronze reward. That made me take a closer look at the other bronze rewards I've received over the past few days, and in so doing I couldn't figure out how the values were being arrived at if the math was being applied consistently. I've attached a series of data with some calculations and questions; please make all this make sense.