Seems pretty straight forward to me, LEM is on the right track.
Its gotta be about clearance with #1 condition lever, but more importantly from both seats!
ie when the skipper puts his RIGHT paw on the PL's his thumb naturally sits off to the side of the #1 PL. No problem, no snags for the full range of fore-aft movement.
When the F/o places his LEFT paw on the PL's, his right thumb naturally sits of to the side of the #2 PL. IF the lever knobs were the same width then said thumb would definitely snag on the #1 condition lever at some point in the PL fore-aft range.
The fix - shorten the width of the #2 PL slightly to give effo Bloggs and his fat thumb some more space.
This being the case, does seem to be a bit of an afterthought in the design process.