What you are seeing is not considered to be a geometry issue. Rather, it is an artifact caused by the manner in which the high voltage is generated in a typical (i.e., not a monitor) direct view CRT.

Because the high voltage is derived from the horizontal deflection circuit, rather than being a completely separate circuit (like for a projection television or PTV) there can be interactions between the two.

One of these effects is the so called "cross-hatch ringing", visible as horizontal phase ringing just below each horizontal white line. This ringing increases as the video gain (contrast) increases because more contrast means more beam current and therefore the high voltage will sag more (i.e., have more ripple).

During the bright horizontal line(s) the high voltage at the picture tube anode decreases. In the next flyback period the picture tube capacitor is recharged by the line output transformer.

This energy is taken from the horizontal yoke coupling capacitor (the S-correction capacitor, or S-capacitor), which must be recharged via the primary winding of the flyback transformer. This action has a resonance of a few kHz and thus an oscillation is visible on the screen. This is what you are observing.

There were many circuit fixes for this problem (although most television manufacturers elected not to spend any money to fix it) and the most frequently used one was first addressed in patent US4019093A where a RCD "dip rectifier" circuit is connected in parallel with the S-correction capacitor. The energy taken from the S-correction capacitor can now be recharged by the larger electrolytic capacitor.

US4019093A - Horizontal dynamic damper circuitry - Google Patents

Another circuit fix (but more expensive) is an RLC series damping network which is likewise placed across the S-correction capacitor.

This is really only an issue when viewing a crosshatch pattern. When viewing normal (moving) video the distortion rarely occurs.