I've started to wonder how many subcontracotrs there are for Esbit tabs. I've found that the older, military packed ones (three tabs in a yellow plastic and foil pack) work better than the newer, civilian style ones (red and silver with clear plastic individually wrapped ones).

One thing that I've found helps them is a reflector under the stove, along with side pieces. Mine are aluminum foil, and while I have the same problem you do with a pint of a water, I can get it hot enough to have bubbles up the sides of the pot.

Have you tried using the tabs with an alternative burner, such as this one?