I've actually watched this fighting B'ger, if you stay low above the hull and level yourself there's a small area between the spikes where you can target both forward and rear torpedoes (you can see this easier with the Borg transwarp gates, but no shields so they're not a good example). When you're there energy weapons seem to hit all four quadrants, but more on the ones your bow and stern are over. If you move a little bit out of there, you'll be hitting the quadrant you're above.
If you really like to see what happens and want to be save while doing so, your best bet is with a Tactical Cube. Fly above and you'll see that your weapons hit the shield facing you are closest to and you'll see that both your front and aft weapons will shoot it. The Cube is large enough so you can circle while hitting only 1 facing with half speed in an escort. Below works the same way, but I feel more comfortable above my enemies head.
For B'ger it's a bit more difficult to see where 1 facing ends and another starts, but the basics are the same.