[Elecraft] KX3: Roofing filter behavior

[Mike]

Hi, 
It is written in the manual (p. 39) that:
"Roofing Filter Configuration for SSB Mode: Roofing filter FL2 (3 kHz) can be
inserted when the upper edge of the receive passband reaches either 2.4 kHz
(default value) or 2.9 kHz. When the passband edge is higher than this, FL1 is
used (wide filter). (If no KXFL1 is installed, FL1 is always used.)"
Indeed, when I set it to 2.9kHz the FL2 switches exactly at that point. But when I set it to 2.4kHz, the FL2 switches at 1.7kHz. I made a video clip showing that: https://youtu.be/bh3xZxrxhko.
Is there any explanation?
Thanks,Mike AB3VN