I have done a lot of thermal printer developments so hopefully I cn help you.

One of the biggest problems with a thermal printer is thermal management. You basically have to ensure each dot reaches a certain temperature as rapidly as possible and stays there for the right period of time. The amount of energy needed to do this depends on:

1. The average temperature of the head as a whole
2. The temperature of nearby dots.
3. The number of dots fired.

The thermistor gives you a reading for the first factor and can be used to reduce the print stobe width as the temperature increases (the data sheet should tell you by how much).

Using several strobes so that dots right next to eachother are never fired together is how the second problem is addressed. You should therefore ensure you do not simply strobe in the order 1,2,3,4,5,6 because you fire dots right next to ones that were fired on the last strobe. Instead you need to use a firing sequence like that used in a 6 cylinder automobile e.g. 1,3,6,4,2,5

Lastly the thermistor has a relatively slow response time so it cannot account for the instantaneous energy input by each strobe, the value of which depends on the number of dots fired in each strobe. Printing all black dots raises the temperature a lot more than printing just a few so if you print a lot of black dots on one strobe then you need less energy for the next strobe. Again the data sheet should provide the figures for your head.

Ian