Well, i wanted to try if i was right. So i drill several holes in a new capsule, to form a pressure-gradient capsule, effectively transforming it from an Onmidirecctional capsule, to a Figure 8/cardioid capsule.
Surprisingly, i didn't damage neither the FET nor the membrane. I cleaned all the metal shavings with compressed air and I wire the capsule to test it with my zoom h6.
I used a 500hz tone coming from a single speaker. I could hear a clear difference in the level of the sound when I rotated the capsule.
Sadly the high noise-floor of this configuration made difficult to measure the level in the recording.
Audacity shows about -5db off axis.
This could be improved with a better preamp and the interference tube.