Cloaking Device: Arsenal Control

[Perfidy]

Against the skulls in a mission, it seems the 90 feet of stealth from Cloaking Device does not suppress when attacking as the description suggests it should. It remains at 90 ft. 
There were two skulls in very close proximity; I shot at one, defeating it. The other continued to read/write on a clipboard - which is not normally how they behave. Typically, the 2nd will take note the first one is taking fire and respond with their own attack. At least, that's always been my experience with NPCs. 

[Frozen Burn]

If you remain at max range, it is possible to pick off mobs one-by-one without aggroing the whole mob if the other mobs are not facing or can see the one you've killed.  So if Mob #1's back is to Mob#2... you can kill Mob#2 without Mob#1 noticing and aggroing. 

 

So, your stealthiness may have been suppressed as normal, but you were still far enough away and the Mob may not have witnessed or "heard" his fallen brother/sister.