I think the "same size or slightly smaller than the girth" is a bit overused.
You can feed multiple small rats as easily as you can feed one larger prey item.
I feed all my adult BPs multiple small rats. I mostly feed the adults 30g - 40g rats... just figure out how much your snake should be eating in a feeding and do some very simple math.
Two 40g rats (or even four 20g rats) are going to put your snake at less risk then one 80g rat.
Invest in a $10.0 digital scale and do not guess on prey sizes. Once you get good at it, then you can start eyeballing them and figuring out weights.
I used to take mine to the feed store to weigh my live feeders. You may get a few odd looks, but *meh*...
Bruce
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