Hi 178
The reference is AMC1 ORO.FC230(b)(1)(iii) is the reference and states:
(iii) Once every 12 months the checks prescribed in (b)(1)(ii)(A) may be combined with the proficiency check for revalidation or renewal of the aircraft type rating.
I realise that is not 'technically' in the regulations but hope that helps.
Cheers
TeeS