Conceal Shot 5 (Source)

Not only is cover not necessary for Concealshot, it does nothing for you with Concealshot. Read the description, cover only adds to your (ranged) defenses; it does nothing to make you harder to see. Also, if you are in cover and do not have Concealment 3 to get Sneak, you cannot do a Peace or move while in cover. So Cover is not that useful unless you are fighting someone who is shooting at you, and it can actually be a detriment when using Concealshot.

The keys to remaining undetected are: the further out you are, the harder you are to detect, and the lower your posture, the harder you are to detect. Also, as stated by someone earlier, there is no need to do a peace after Concealshot unless you are low on mind, in which case, you should not be attacking until your mind recovers anyway.

So, get out as far as you can (generally around 60m, depending on your gun). Go prone, but do not bother with cover. Check your aim modifier (the number by the target HAM bars. The closer this number is to +50, the better. If you are not at your weapon's optimum range, you may want to move up or back to improve this number.

When ready, queue up at least 3 Concealshots. And be ready to do Peace or queue up more as necessary. I have a macro that does every time. Three is a good number because, by keeping at least three in the queue, you have a few seconds to decide if you want to hit peace or queue up more after each shot, and, if you get distracted for a second, you do not end up inadvertently firing a normal attack by accident.

As a lower level rifleman, especially if you have little from the Sniping Accuracy line, you may want to included /AIM, if you have it, before each Concealshot. This will also improve your accuracy. At Master, this becomes moot.

The things you will want to watch for are:

1. If the target moves closer than 40m from you, stop shooting and crawl further away before continuing. Closer that 40m drastically increases your chances of being seen.

2. If you miss twice, the target will see you and attack. You will want to get up and switch to a faster firing, lower HAM special than Concealshot.

3. There is a random chance that any attack will start a small random bleed on a target, including Concealshot. This likely has to do with wounds, so it may be less likely with a lower damage/lower wound % weapon. However, if the bleed does start, as soon as the first bleed ticks off, you will be aggroed. So watch the target status and if a bleed starts, be prepared to be seen.

Other than that, they added a Concealment chance modifier to the tree. Thus, at the lower levels, you are more likely to be seen than as you progress, so you will just have to optimize your chances as indicated above and live with the fact that they will sometimes aggro even with Concealshot.