I'm using a verticle blend texture to change the size of the particles the more they go up, to mimic a stylised blocky fire. It works, but the starting size of the particles change over time as well. So it looks like the "fire" is getting bigger and bigger over time. While I want it to be a constant starting size, and getting smaller the more it goes up.
Use the method explained here. In the file you share the problem is probably that your gradient is vertical when it should be horizontal: