Don’t know if this has been clarified already, but the Su-27 we’re getting is the Su-27S. The IRST ball is mounted centrally. This is the case with any other early model like the trainers.
See here:
Spoiler
On the other hand, the Su-27SM (with R-77 and A2G capabilities, a mid-life retrofit/upgrade) and beyond, they have it angled to the right of the canopy.