Originally Posted by patelbadboy2006
but won't smaller holes burn the shisha quicker?
It's the opposite actually. Larger/more holes allow for more heat transfer.
I would avoid messing around with your hookah and bowl setups if all you want to do is restrict flow. The only thing I would do is add a diffuser if you haven't already. Water level doesn't make much of a difference on draw.
I'd recommend concentrating more on the hose so you don't affect how your hookah smokes as much, more so the draw only. Try using something that reduces the hole size of the mouth tip, like a male plastic tip or a piece of electrical tape over the hose tip end with a smaller hole poked in it.