Why is the IRST not centered on the Eurofighter Typhoon?
The Thales UK PIRATE IRST system is located here in order to allocate space on the starboard nose for the retractable in flight refueling probe.  The port space was the only available real estate for this avionics to fit.  Other aircraft like the MiG-29 have similar restrictions in space availability.

The asymmetric location does not affect functionality; the IRST seeker head does maintain full field of view without blockage from the nose or fuselage.