I had the original OOB before Taz posted it and BRDM Was amphibious so this may be an oversight.
Not convinced M901 is amphibious in so much as it can just start "swimming" with little or no preperation !
The 2 hex range for the T-80 is due to the laser rangefinder fitted to it not the ATGM systems. The limit of the rangefinder on the T-72 was approx 2000m hence the 1 hex range.