The idiom get your head around something is probably a (dead) metaphor. If so, I'm wondering what the exact meaning of "around" is, literally. There are several senses of the preposition around. I am not sure which one is being referred to by this idiom.
Please go over the senses of around listed below:
Sense 5 seems to be a candidate:
on the other side of something, or to the other side of it without going through it or over it
I'd appreciate your help.