With a straight 44 mm head tube, the taper will be provided by headset.

But it seems that modern high end bikes have a tapered internal head tube to match the tapered steerer. From Specialized, describing the SL4:



TAPERED, SHAPED HEAD TUBE

WHAT Strategically designed head tube on SL4 frames tapers from 1-1/8” at the top to 1-3/8” at the crown and facilitates massive top and down tube junctions.

WHY Increases strength and stiffness for greater steering precision and responsiveness during out-of-the-saddle efforts.

HOW The wider base creates a stiffer, stronger junction, and the gradual transition of carbon fiber from top to bottom eliminates the potential for weak spots due to sharp angles—carbon is at its best when it keeps a smooth line. Uber-oversized top and down tubes “wrap” around the front of the head tube, creating the ultra-stiff “bulges” at the junctions. The design requires a smaller lower bearing (compared to last year’s 1-1/2”) which saves weight.

And here from Parlee:



Tapered head and steerer tubes: An innovation derived from the now industry-wide CEN testing protocols; tapered steerer and head tubes are hardly news anymore, however, with our Z5, we pioneered the use of the smaller 1.250” (32mm) inch lower standard over the heavier 1.500”(38mm) inch standard. Riding the bike demonstrates that the 1.250”(32mm) taper provides the ideal balance for a road bike. Strength, safety, performance and lightweight without harshness.

Parlee, like Calfee, obtains its tubes from ENVE, and the 1.5-1.25" Parlee head tube taper matches the ENVE Road Disc Fork. So, if I am to get a head tube transplant, I think that I will be asking about the tapered head tube that Parlee uses, rather than a straight 44 mm head tube.