Actually the problem is that I loose the Carrier Sense before I loose my packets.
I output the CARRIER_SENSE and the PKT_SYNC_RXTX on GPIOs and when I do a test range, I see an activity on the CS up to 300m (for example in my test condition), while the PKT_SYNC_RXTX still working up to 700m !
My goal is to save a lot of energy without cut the range, so I want to use the CS to wake up my RX and catch a packet, but CS is not enough sensitive to have the full range.