Okay, so I am replacing this last post, because I stand corrected. The "E" series Drake (1.28gpf) uses a different flapper than the "S" series Drake (1.6), which makes sense because both toilets use the same china tank. So you can't use the Korky 2021BP (Red) "Fits Toto" flapper on the E series Drake (and presumably a bunch of the 1.28gpf toilets), at least not if you want it still to be a 1.28gpf toilet.
HOWEVER, it turns out that the current manufacturer's-specified flapper for the 1.6gpf Drake CST744S is model THU331S, which is the very same flapper now being used on the Ultramax II. Presumably both toilets require the flapper to close at the same water depth, although the tank shape is different and less water goes through the valve on the Ultramax II at that water depth. SO, even though the Red "Fits Toto" 2021BP flapper (the equivalent of the Toto THU331S) was originally designed for a GMAX flush, it is a correct replacement flapper on the Ultramax II. It has become a little hard to find since Korky came out with the adjustable 3" flapper; you can carry the correct replacement flapper for all 3" Totos just by carrying that. So, for example, Lowe's shows the 2021PK flapper on it's web site, but it isn't available anywhere in the New York area and isn't available from Lowe's online. Plainly, they are shifting over to carrying just the adjustable one. Same with HD, who actually sells it online-only for a few cents more than the adjustable one, which it sells in stores.
So, for the original poster, you did the right thing by getting the adjustable one, and its setting should probably be "6", the same as the Drake ST743 mentioned in the instructions (which is presumably the 1.6gpf version of that tank). See how that works and let us know.
CLIFF NOTES: The Korky Red "Fits Toto" GMax flapper, 2021BP, is an acceptable replacement flapper, surprisingly-enough, on the 1.28gpf Ultramax II, if you can find it. (It is also acceptable replacement on the toilets listed below.)
The Korky Adjustable 3" flapper, 3060BP, should work well at a setting of "6" on the 1.28gpf Ultramax II. However, verify this by marking the water level where the old flapper closed and see if the new flapper shuts at the same water level when set at "6".
EXTRA CREDIT: Here are all the Toto models, new and old, per the Toto Tech Support parts spreadsheet, that use the THU331S Flapper and thus should work just fine with the replacement Korky 2021BP Red "Fits Toto" flapper (and/or a setting of '6" on the 3060BP Korky adjustable 3" flapper):
ONE PIECE:
Aimes Flapper
Carlyle (original) Flapper
Carlyle II Flapper
Eco Guinevere Flapper
Eco Lloyd Flapper
Eco Soiree Flapper
Legato Flapper
Ultramax (original 1.6gpf) Flapper
Ultramax ADA Flapper
Ultramax II Flapper
TWO PIECE:
Carrollton Flapper
Clayton Flapper
Drake (original 1.6gpf, not the "E" or the "II") Flapper
Eco Promenade 424EF (1.28) Flapper
Mercer Flapper
Pacifica Flapper
Vespin (original) Flapper
Whitney Flapper
The replacement Korky 2021BP "Fits Toto" Red Flapper, although not at HD or Lowe's, but it's likely cheaper in the end to just get the adjustable one, 3060BP (or PK or CM, at L and HD, respectively) at Lowe's or HD or your local hardware store.