Help with BB size replacement

NOTE: most BB-axles are not symmetrical.
That means, if the length is 10mm shorter, it's not 5mm on both sides.
So, the chain line does not necessarily move 5mm inwards.

According to my LBS that is exactly what it does: 5mm shorter IS 2.5mm each side. I actually watched very experienced guy swapping out my BB to get a perfect chainline and mumbling, "Well, if we need another 1mm off there I want to come down from 115 to 113." But yes, they are of course asymmetric.