Actually it makes more sense. The overheat duration is the same as wildfire. Basically you would like to stay between 50-90% while your wildfire is on cd, and then go nut once it's up. using ammo helps you balance that heat.

Reddit got some interresting theory crafting, i'm really happy with all this change actually. There's no penalty anywhere if it's like this, just a deeper cd management with the heat management. Also, you can see where you can put our new dot (the flammethrower) to build up heat but not to much so you're not busting your wildfire