A tighter grip isn't going to change where the pressure is concentrated. A light, but firm grip is best IMO. If you want to change where the pressure is, just break your wrist a little more, i.e. heel the bow a little more. But if it feels good to you where it is, don't worry about it.
There are lots of different definitions as to what constitutes a low wrist. Here's mine. A straight grip like on a Howard Hill or Great Northern is a true low wrist grip. On the other hand, a lot of locator grips are also configured in what is called low wrist. These have a carved out/indexed area immediately under the shelf with the palm area slanting toward the heel of the grip area. They are quite common on hybrids. The lower the angle of the slant, the lower the wrist, or conversely, the greater the slant, the higher the wrist. Even in so-called low wrist configurations, this grip has a tendency to push/locate the bow hand into the index and concentrate the pressure at the base of the thumb and forefinger.