On sensitivity of 6-9 I find the XT2 cameras trigger immediately at 6 or 7 metres as a person enters the frame from left or right which suggests the PIR sees it even slightly outside the video frame and sets up the recording to start once the person first shows . This is also ‘across camera frame’ movement which PIRs are quite good at detecting
I find approaching the same camera directly (from any angle) from a distance doesn’t trigger the camera until quite close. Say 3 or 4metres. This approach looks like a target growing in temperature or size in the PIR detector and they are not so good at seeing that as movement.
Camera Positioning vs likely approach routes is therefore the key. Range improves a bit as you increase sensitivity 6 -9 but at the same time sensitivity to moving bushes and birds, midges etc. increases a lot. Decide how many false detections you can accept and take that as maximum sensitivity.