The default thruster config has been changed in 0.154 to a linear scalling instead of box dimensions:
- Box dimension: increases with the box dimensions of the thrusters, same mechanic as power. This system was introduced in version 0.14
- Linear: The value increases with the amount of thrusters, no matter how they are placed. I believe that this system was in place with versions 0.13 (and under) and is back as the default setting for 0.154+