If you have the sport package on your 07 then you have the active suspension. As for setting the "active suspension tow mode" i was told it was an automatic function when the car has sensed that the rear suspension has been lowered due to weight and the car will jack or raise itself up. I know I have noticed when I started loading the car up with full coolers that the car would jack it self up automatically once I put 10 cases of beer, ice and booze in the rear with people in the back seat.

What does not make since is why it is not consistent. This may be a stupid question but were you on level ground when you measured? The suspension may have been trying to compensate for the angle.

__________________
2012 X5 50i ZAP(2VA, 336, 465), ZTP, ZPP, ZPS(6VC), ZCW, ZRC, 322, 4UB, 4NC, 610
2011 ///M3 Silverstone II
2011 X5 50i(lemon)
-- SOLD --
08 550 Msport
07 X5 4.8I sport
04 545i sport
02 4.4i sport
01 540I M/sport
00 SL500
97 SL500