Pantheon Spear Shot mechanics

I've been doing some research, but no luck thus far. I thought I'd pose my questions to the boards:

Can Spear Shot critically strike outside of the 15% of maximum health threshold if critical strike chance has been purchased?

Does the Infinity Edge modifier impact the damage dealt by Spear Shot when a target is below the 15% threshold? Does this function the same way for basic attacks?

Thanks!