To use layman's terms, the prostate is adjacent to the "front" side of the rectal wall, as shown in the illustration below. It is a few inches past the anus, so that a finger can reach it.
Stimulation of the prostate by the penis can be affected by any curvature it may have (my own is almost perfectly straight). For men who have an upward curve when erect, the missionary position (facing each other) may work best, rather than doggie style or any rear-entry position.
The missionary position also places the most prominent part of the ridge of the penis head (the corona of the glans penis) in the best location to rub against the prostate. Since some bottoms don't want too much prostate stimulation, if it's overly sensitive, they might prefer contact with the underside of the penis instead, which would indicate a rear entry. Plus another factor is the relative size of the glans penis, some men having a very large mushroom head, while others have a head smaller in circumference than the shaft.
Knowing the front location of the prostate it's not difficult to understand the best angle of entry to hit it. At the same time, for a top with a very thick penis this topic may be largely academic, since he'll be stimulating the prostate no matter what position and angle he uses.
With all these variables, each top and bottom must experiment to find their own best solutions. So that the answer for you may be different with different partners. In general for me, however, since I have a prostate liable to being tender, when bottoming I prefer to use the doggie position, which I've found is least likely to cause me discomfort.
"Is it all about the feeling that the prostate gives when it is being massaged/banged that makes bottoming so good?"
For some men, yes. For me, not so much. Having a tender prostate the pain often overcomes the pleasure. I bottom more to please the other guy, and get a psychological thrill from what he's doing to me. For me it's sorta like docking: not really physically stimulating, but a mental rush. And if he's versatile like me I'll get off by topping him, or he can blow me or jerk me off. I'm really not very particular. LOL!