Ah, but if you had a book entirely devoted to port, say, The Port Companion (Canada, UK), perhaps, you would indeed find the reference you seek. The author Godfrey Spence, says there is no one correct glass. Because the alcohol content of port is higher than most wines, he says, it is served in small glasses (where you might get six glasses from a standard wine bottle, you should get 10 to 12 from a bottle of port).
However, Mr. Spence respectfully says your great grandfather was all wet. He says small Paris goblets, small versions of the Savoy glass, and the inexpensive tasting glass of the International Organization for Standardization are all appropriate for sipping port. The common feature of these three is a relatively small bowl that slopes in. With a flared glass, “the all-important bouquet is lost.”