Yea, this is definitely an issue, I changed wood to burn a lot more slowly, but what happens is once a fire reaches “raging” it just goes totally out of control and starts burning through its fuel much faster. Another problem is once it reaches raging, I don’t think it goes back to medium intensity, because it starts consuming fuel even faster, so it just suddenly dies out.
In the current system, your best bet is probably to try and keep the fires from reaching the raging point, by spreading them out a bit more, possibly a checkerboard pattern? The number of adjacent fires does influence the intensity of each of the fires. Partially so that you can more easily make a single-tile fire without it getting out of control, but still let burning buildings turn into a raging firestorm.