Chipshouter - Minimum pulse width

I have a problem finding the exact tuning of both the amplitude and pulse width to get the shortest pulse possible with the 1mm injection tip (15 ns) and also the 4mm tip (24ns) as mentioned in the datasheet. For me, the minimum pulse width I was able to achieve was 31ns after sweeping various voltage amplitudes and setting the pulse width to the min possible either with basic pulse generator or the programmable pattern generator (20ns/0110). I even used two different properly calibrated oscilloscopes but the issue remained.
I was wondering if the values mentioned in the datasheet represent full width at half maximum (FWHM) and not the full width (from rise of signal until it comes back to 0)?
Any details on this matter would be highly appreciated!