If your levers are not coming all the way back and hitting the bars the only thing that adjusting the cable to be loose or snug does is set where the lever sits when the pads touch the rims. There's no difference in leverage either way. If you seem to think you're pulling harder to stop when the cables are more slack then it may be the way your fingers are sitting on the levers in one position versus the way they sit on the levers when the cable has less slack and you're using the outer part of your fingers.
If you're looking to get the brakes to work with less finger effort you may want to try shifting the pods inwards on the bars a bit. That way your two fingers that you are using for stopping will be at the end of the lever more fully where they produce the best leverage. As a side bonus the levers are in further and run a slight less risk of damage in a fall. Give it a try and see if you like it. I know that on all my bikes the lever clamps are spaced in about 3/4 of an inch from the ends of the grips just to give my two braking fingers the best grab at the end of the lever.