The problem with the damper cap trick lies in the old adage "there is no free lunch".
The higher the value of the cap, the more width you get, but the plate current of the H.output tube diminishes. This reduces the "stiffness" of the HV supply, and the HV will sag with CRT beam current and the raster will start to bloom as you turn up the brightness.
So the cap trick is a balancing act between width and HV regulation. Often you have to increase the G2 voltage on the output tube to improve HV 'stiffness'.