The issue is not whether you only mine "1 BTC of buy orders for 1000 CGB", but buy orders at what price? Do you only take into account buy orders that are more profitable than mining the next best currency, or which specific buy orders? I would strongly argue that only buy orders that are at a price near/above the point that represents the next best mining opportunity should be mined/filled
I don't quite understand.
But the way I do it is this:
As we mine CGB, our CGB balance increases. When checking the CGB price, I discard the top X buy orders of CGB, where X is our balance plus the amount we'd mine in a few minutes. Then the next buy order on the list is the price I use.
I do this for every currency, so all the prices are "volume adjusted".