I hesitate to post this because my opinions could be wrong. It's also a possibility that the creator of the AKM style brake could come on here and embarrass me with my childish conclusions.
Anyway, I've tried the AKM brake on both a 12 inch and 18 inch rifle and on both it's compensating effect was vigorous. The one I have is actually different than the one pictured on the Dlask web site. It has a band milled around the midpoint of the device.
At first glance, the AKM brake looks simple, but IMO it's not. I believe a lot of thought went into it and it's actually very elegant in it's design. I've found this to be the case with the Dlask A6 as well. If you know what you are looking at (and I'm not saying that I do), there are actually some very subtle features that you don't see in other designs. They didn't just take some round bar stock and cut some random baffles in them. Someone spent a lot of time on these and took great care to do things right.
But back to the AKM brake. It you look at the brake top down you see a stepped expansion chamber, open at the top, and leading to a grove for the bullet to pass through. Surrounding that is the "slant" potion of the brake. This area is not just cut with flat edges but those edges are concave in nature, I assume to increase surface area and catch more gas.
I believe the expansion chamber step actually provides some small braking effect as the step would act like a small baffle. The step would also push a large portion of the escaping gas upwards at an angle. Since expanding gas tries to go in all directions , the concave surfaces on the "slant" portion catch some of the expanding gas and provide more compensating effect.
Cutting the device back from the front would start messing with the bullet path grove and the other concave surfaces. If I were you supernova, if you tried cutting the device back, I'd carefully watch how these changes affected accuracy. If you went too far, you would mess with the expansion chamber and step, which would really mess up the function of the device.
If I wanted to mess with it, I'd probably try to turn down the outside diameter of the front portion of the brake ahead of the band. This would take surface area away from the concave sides of the slant cut. Which may help limit the compensating effect. If that didn't work, the other thing I would try would be the increase the size of the expansion chamber and slightly reduce the angle of the step. But that would be much more complicated.
It should be noted that the original AKM brake was clocked to the right a bit to prevent muzzle climb. I never tried doing this with the Dlask one.
I'll be watching this thread carefully as I'm very interested in the results.