FWIW: some of these differences are not about the mike's electric principle, or really about size.
A small omni can be "flat" at any distance.
The basic Directional (cardioid or fig-8) principle is elegant and valid for "distant" sources, but gives bass-rise on "small near" sources.
You can just enjoy it.
The mike designer may optimize midrange, let the far-bass fall-off, so that bass-rise on near sources is not excessive, and distance becomes a useful balancing tool. This works well on Dynamics.
The designer can tune for "flat", and give you bass-cut switches for close-in work. A condenser naturally wants to be flat, so this is what you usually get.
E-V had the "Variable-D" principle, with a more complicated back-path, which gives much less bass-boost on close sounds. Good when you don't want the "Sinatra balls" come and go as the talker sways back and forth. (However many professional talkers, such as O'Bama, learn to use an SM's bass effects to emphasize their speech.)
And any of these effects can be done/un-done with a flexible bass control on the recording system.
> close-miking on moderate overdrive sounds is for the birds. Even Shure's manual recommends 6 - 12 inches for a full balanced sound on a cab with an SM.
Cones have significant proximity effect too. If you get the mike less than an inch from the cone, you get a very-near-field sound that you never get in the room. From there out to about half-diameter (say 6" on a 12" cone) there is a near-field sound which varies from place to place, still "not normal". Out beyond about 4 feet you get Room-Sound, the basic balance heard when you play.
Close-miking is over-used. If you do not have other sources in the room, and your source is loud, you really should try 3 feet and 8 feet out. True, if you have other amps or a drummer, you "need" to be close for isolation.... or actually listen to what is happening in the room and adjust placement for good blend.
> I tried 12 dead center and it sounds much better.
Sure. But you may find that "dead center" has strong focus points, and a small change of mike placement gives a large change of sound. Conventional wisdom is to set 1"-2" OFF-center.... you don't get hot-spots that come and go when the stand gets bumped.