With MES2 and the support skills fully invested in, I've been able to get within 3.5-4km of someone before being detected. The disparity is either due to the targets investment in sensor skills and consoles, or their reaction time.
The other day I was going to happily blow up this nice little science ship, which clearly had a chewy inside, and a soft outside, when suddenly the damn thing disappeared as if cloaked. Was I hit with Jam sensors, or was that EMS or something else equally annoying?
Since then I went ahead and re-got myself science team 1 to stop the nonsense but I haven't been hit with the thing again..