The HSYNC is modified before being sent to the monitor. It happens 2µs after activation of the CRTC HSYNC and stay a maximum of 4µs (signal is cut short if HSYNC width is greater than 6).
For example, if CRTC R2=46, and CRTC HSYNC width is 14 chars then monitor hsync C-HSYNC starts at 48 and lasts only until 51 included.
On Gate Array, even if the duration of the CRTC VSYNC is reduced to 2 µseconds, the Gate Array will always output black for 26 lines with 4 lines of C-VSYNC to the monitor. While on ASIC/Pre-ASIC, the CRTC VSYNC must be active for the C-VSYNC signal to be sent by the ASIC to the monitor.