There is, admittedly, some variance in IM seatpost diameters. All of mine have been 27.0, across 85-86-87-88, but know that others have used a 27.2…although don’t know if those were from the factory or aftermarket fits.

At any rate, better to buy a new and longer post than have the insertion line above the lug. It’s there for a reason and put there by smarter people than us. Well, me, anyway.