While lower brace height can add some cast to the arrows, there is a limit. It really isn't a function of draw length per se. You won't be able to drop it enough to offset a 3-4" shorter draw.
Too low can cause some problems as well. The bow will be louder. You may (probably will) experience string slap to the wrist, which can increase noise and cause erratic arrow flight.
I would try to stay within the recommended brace height for your bow. Dropping the the lower end of that would be ok, but going much lower is going to be more hurt than help I think.
If you are concerned that you aren't getting enough speed/penetration, you may need a higher draw weight bow. If you short draw by 3-4" you lose 9-12 pounds of draw weight (approx.). Use that to estimate your actual draw weight, then select a bow that gives you the desired draw weight.
Hope this helps.