First and reverse aren't synchronized. So they require double clutching. Usually with reverse I stop the vehicle, see if it goes in reverse, if it doesn't, put it in neutral, release the clutch a bit, then depress it again and see if the gears are aligned then. Reverse is "all the way out there" though, quite a long throw to the right and then front.
Because the engine is kind of reversed in the BRDM (gearbox aiming to the front, ancillaries attached to the radiator/rear side) the gear shift pattern is also reversed.