Going from memory here, IIRC it's as simple like taking some evergreen strip, gluing it above the current weatherstrip and then removing everything below, thus enlarging the opening, the only thing that remains somewhat of a problem, is the glass itself, cuz while it still fits, the upper area gives optical distortions.
On one of my talks with a Amt top Kat, back in the day, the molding facility was to blame for that, it had something to do with not having window trim on the tooling model, because the tooling company engraved it while machining the molds...again going from memory here.