My suggestion is to add a bit of heat output for every block placed.
Currently there is little holding big tanky drones from taking over online matches, this is due to the fact it is very easy to have maximum DPS, high health, good speed and cooling all at the same time.
I think adding a small amount of heat for every block placed could combat this issue.
How would this solve the issue?
In short, the more blocks you use (and thus the bigger the drone) the more heat you will produce no matter your component use. This forces big drones to invest more in cooling.
This takes away from other areas like shields, weapons or movement seeing energy is required to power the cooling.
To start off I'd personally say add +.1 heat/block.
TLDR: This adds more heat to bigger drones, which forces them to use more cooling and have less invested in for example movement or shields.