Paul, obviously our "guesses" are all theory based on what and how we catch them, but I think RW's comments above are a good starting point. In a current situation like a river or a TVA type impoundment where they generate water, angles are very important. From a general structure point of view on a non-current lake, then I think you have a few scenarios at play.
One is RW's thought about there to feed and just being in close proximity. That works for groups of feeding bass or bass that are what I would call above baseline as to feeding stimulus or mentality. These are the easiest of the situations. Bass, whether individuals or small packs moving up on top of structure or along edges looking to feed can often be triggered just by getting a bait near them.
But there are a lot of possible specialized scenarios. One is pressure/conditioning. Bass get used to seeing baits worked from the same direction all the time on certain lakes. One in particular near me comes to mind. Throw shallow and work deep only works on the "easy" days. Most times if you throw deep(er) and work up the break, making more contact and creating more disturbance, you'll catch bass going right behind other anglers.
Another is individual bass sitting on individual pieces of cover. A single large stump on the edge of a point as an example. If that fish is neutral or inactive, he is probably sitting in a very specific spot in relation to that stump, facing a certain angle or direction. He may or may not see your bait the first time through. If you're moving along you could easily pass right over with the wrong cast and never know that fish existed. If you know that stump is down there though, you can take your time and slowly move around that stump throwing from different angles and trying to figure out exactly which one will trigger the bite.
That "trigger the bite" deal is the whole key, especially for groups of bass. You really need to play with everything from bait types to angles to retrieve styles trying to figure out how to get a bass to react. So many times if you get one bass to bite, that triggers the group and they all start looking. Their baseline attitude goes up quickly. Then it is a matter of speed and efficiency, because often you'll start pulling those other fish away from the structure/cover as you keep hooking bass. Others actually follow or compete, making short dashes looking for the next meal to target. When I post those pics on my site of doubles (or make mention of that), that is a perfect example of this. One bit, another one moved with and tried to outcompete the other for the same bait - both get hooked 8-) There are probably more down there with them. They're not going to go back down though and sit all perfect in relation to a cover object. At that point they're looking to feed and just getting close as in RW's comment then applies.
The deal for me is always taking the time to thoroughly graph and understand an area the first time I come across it. I want to know where the bottom changes are, where the cover objects are, which side has the sharpest drop, how flat and at what depth is the feeding shelf, etc. Once you have that compete mental picture, you can then not only formulate an initial approach based on how you think is best to fish the location, but you can also visualize alternatives if that first approach doesn't work.
As individuals, bass have certain personalities on any given day based on all the existing weather/water/forage conditions. Some days paralleling the break doesn't get it done, when banging the bottom perpendicular until you fly clear of the break into open water does. SOme days your bait never hits the bottom before it gets intercepted, other days you'll never get bit unless you literally hit the specific "break on the break". That to me is the fun part of deep water fishing.
-T9
