Scar tissue can have odd nerves. Lack of feeling, or, hypersensitivity. Lack of blood flow etc.
There are several things that people seem to respond to as far as "getting relief" from cutting. Pain, blood, the way the skin opens with a laceration. You probably don't get those with a lot of scar tissue. I don't know for sure, but you probably don't get the endorphin rush you do with fresh skin.

Even if you were cutting in several different areas that were not scarred, chances are you would eventually find that shallow cuts no longer made you feel better. Cutting is an addiction, and like every addiction, tolerance builds. In this case, to endorphins.

The best thing you can do is seek help and find a less damaging way to handle your emotional pain. You have to live with those scars for the rest of your life, and though it may not seem like a problem now, your life may change dramatically later and it will matter. Besides that, there is always a chance that you may damage a nerve or tendon inadvertantly and cause permanent disability to a limb. At best, cutting is a very temporary way of easing your emotional pain. I cut for decades before almost killing myself by cutting some major vessels. It didn't start out that way, but now there are areas in my leg that are numb while others are hypersensitive. Even to the touch of a pant leg. Do yourself a favor and get help. You deserve better.

Sam2