Seems that there is some confusion about profile dampening. Snipers should be using profile dampeners for covert sniping, frontline KTac quickscopers should stack EHP.
Profile Dampeners reduce scan profile of the dropsuit, as stated before they keep you off radar while in range (close range).
At distance though the whole staying off the radar becomes irrelevant.

BUT profile dampeners do something else, while in direct line of sight of an enemy you become 'lit-up' on the tac-net. Basically if one enemy can see you the whole team can 'see' you 'spotted' on the HUD. A big red chevron is displayed above your head and remains until your dead or the enemy stops looking directly at you.

If you use a profile dampener that drops your profile BELOW the spotting enemy's precision you will NOT show up on the tac-net for all to see. Yes the dude looking right at you will still 'see' you, but now the 15 other snipers on the team wont know you are there unless he verbally ID's your position or they physically look at you.

Breaking the profile dampening stacking idea with numbers: Cal Ass suit has a profile of 50. Scouts have 45 precision stock. So if a scout see's an assault, then EVERYONE does on tac-net(HUD). Now lets factor in an enhanced profile dampener on the assault suit, the skill required to use the module grants 6% reduction in profile while the actual module provides a 20% reduction for a total of 26%. 50(assault suit base profile) X .26(26% bonus reduction total) = 13(total reduction). 50-13=37, 37 being your new scan profile. Now remember a scout suit unbuffed reads at 45 precision, with a profile of 37 you will remain off the tac-net to all unless a scout is stacking precision enhancers.
That being said stacking anything more than 1 dampener is only useful if compensating for a scout who has stacked precision enhancers(who even does that?). Otherwise one dampener is enough for 90%(random made up number) of anyone in game & still stay off the tac-net.
Same principal applies to active scanners, they cant scan you either when damp'd.

TL;DR: Snipers should have one profile dampener equipped to remain of the tac-net if spotted. Using more than one dampener is redundant. If you see someone 1st you should kill them, if they see you 1st you should die.