Depends on the size of the jib and the location of the turning blocks...
If you are trimming the sheet to the toerail, you probably want to go outside the shrouds.
If you are trimming a large jib like a 150%, you trim it outside because it wont fit under the spreaders.
If you are trimming a smaller jib and have inside tracks, trim it inside the upper shroud or you lose a bunch of pointing ability.
Certified...in several regards...