Here's a list of mods with flat output from an ECF post by DAM718 posted just about a year ago (11/6/13); as far I know, it's still up-to-date. (The post is here:
http://www.e-cigarette-forum.com/forum/variable-voltage-apv-discussion/487745-mods-have-absolute-dc-output-like-provari-3.html) and scroll down to post #28 (If you follow the link, be sure to check out the poster's title.

The Vamo is not on the list, so it is also PWM. I've heard others saying they notice a difference too, and describe it pretty like you just did, GM. A likely explanation is that the peak temperature with PWM is higher than it would be with flat output of the same RMS wattage. Don't know if that's right or the whole story, but it makes sense.
One thing I find interesting about that list is that the Evolv 20 is on it, but its successor, the 30, isn't. The TP 40 (as I call the Evolv DNA 40 with Temperature Protection) can now be added. Plus in addition to temperature protection and a flat output, the 40 also has buck circuitry, so it can regulate below the battery voltage, which the 30 couldn't do either. I can't wait to get mine -- a combination of curiosity, plus trying what seems to be almost universally being acclaimed as the best vape anyone's had.
I'll trade a link to the kayfun thread for the links to two DNA 40 threads. (Not that you can't get them without me. lol) I want a Kayfun and I'm suffering from Kayfun Konfusion over which one to get. I'm trying to keep from Russian into a premature choice. (Ouch!)