I'm 5'1.5, with short fingers, and ride a Specialized Ruby size 44cm. It came originally with 105's that I upgraded to Ultegra SL (along with a replacement frame ) after a crash really messed them up. The Ultegras don't really feel much different, and they have the shims in them that Specialized uses, probably the same as what you have in your levers. It's that bulbous shifter mechanism that makes it harder for me to get my fingers around the lever when on the hoods, and I don't think that the shims help much there, they only really help in the drops.

You may want to get the more powerful hand on the rear brake. Not that it would stop you better, but it might help prevent panic endos occurring from locking the front wheel with the more powerful hand. If your left hand is weak and you feel it would be unsafe on the front brake, as it is the 'stopper', you might want to keep it on the back brake and do some strength hand exercises (like a squeeze ball). I am lucky to have good hand strength in both hands despite carpal tunnel, so run with the right on the rear brake.

If I have to brake suddenly on the hoods, I try to shift my weight down and back, knowing that i might go over the bars if I lock the front and allow my weight to shift forward. I also know that with the longer cable run to the rear brake, and the extra brake housing, along with the weight shift forward with deceleration, that the front is doing most of the work.

The other replies here have a lot of good information. I would also add that when I switched to a better brake than the Tectros that came on the Ruby (I put my old Dura Ace on but you don't have to go that pricey to get a better brake) braking force increased and braking effort improved and eased a great deal.