You don't.

dwell is quite simply the amount of time the points are closed. There is only so much time, because:

In the case of points, or electronic, there is only so much "time" between each cam lobe. Obviously, the points (or ecu) has to be open a certain amount of that time---that's when the spark "happens." So, there is only so much time for each cylinder, that the points can be closed.

In a points system, part of the reason that you can only have "so much" dwell, is because the cam lobe must have a ramp that opens quickly enough so the points don't tend to arc and burn, in other words, sort of "snap" open, so to speak.

This means that so much of the "time" on the cam must be occupied by the lobe and the ramp on each side.

This is part of the reason that dual points were used. The points overlap, so one set CLOSES the circuit, while one is still open, and the overlapping set opens, while the second one is still closed, and opens last. This allows for greater dwell, and leaves each set to do "half the work" meaning the arc and spark is shared between the two.

Dwell for 4, 6, and 8 cylinders was "decided" by many things, including the time envolved, the shape of the cam, point wear and bounce, a number of things.

One electronic igniton, the dwell is set pretty much by the electronics IN THE BOX. You cannot change it. I spose it's possible that if you put a different box in there, it would improve, but it might not, either.

The upshot is, if you have a good hot spark, and the car runs good, leave it be