Recently I got BaseBox2 as a compliment to an existing Omnitik5 AC (I wish I could have just added 2.4GHz card to it).

I have two ACOMNIRPSMA Antennas for the BaseBox2.

The question is: how do I position antennas axially relative to each other?
Looking from the top:

1. -- --
2. | |
3. -- |
4. \ /

I currently have them 90 degrees to each other ( -- |).

The idea is to use polarization diversity to enhance the 2 chain performance (2x2 MIMO) ... space diversity us fine as well, but polarization is better. And polarization is correlated with antenna direction (for most antennae).

Meaning that your current setup is (almost) perfect. The angle (horizontal+vertical versus +-45 degree tilt) which would give some extra performance then mostly depend on antenna arrangement of the other end and mildly on amiunt of reflections (keeping in mind that WiFi performs good only in line-of-sight conditions).

In short: keep things as they are.