To get to the point. These guys told me that by flying in a mulitcrew aircraft you can actually log 50% of the time flown toward the PIC requirement.
Had this discussion very recently. Not 50% of the time, but you can log PICUS for the time you fly as PF which would normally be roughly 50% of your multi-crew time because the Capt and F/O would usually fly alternate sectors. You can get the Capt to sign the log book or your company will provide a letter of verification to the CAA when you apply for your ATPL.