Rear mech identification!
 

Hi I'm looking for some assistance,
I recently purchased a colnago clx 3.0 105 (2012)
And I'm desperately trying to identify if it has a shimano 105 short cage rear mech or medium.
It also has a 12-25 cassette as standard.
If anybody could tell me what rear mech is fitted as standard on this bike or tell me a way of identifying what it is then I would be very grateful.

Thanks for any assistance in this matter.

Looks as a medium.

I am able to run a 12-30 cassette with the same 105 derailleur.