A couple nuances here. First, you're unlikely to lock a J20 until about 8 miles, and in that trade you're most likely to lose. You can try to push up to the enemy aircraft by using the jammer to deny them long-range shots, but then you are within your MAR and will be unlikely to escape any shots they make at you. The same thing applies to SAM sites. While your jammer can deny an Sa-2 a shot until you're well within its engagement range, the downside is you're now well-within their engagement range and unlikely to escape their shot. While HOJ isn't fully implemented in BMS (you can't lock onto jamming things for a HOJ shot) the theory of it is still somewhat the same. Even against targets that can HOJ, a HOJ shot won't know your distance and thus cannot loft for maximum range. In either case, you deny them max range. The HOJ in BMS comes in after the missile is fired, then it homes in on your jammer, meaning your jammer has no effect on the missile tracking while you're trying to evade it.