well, in my opinion, the whole thing about secondary tweets, or so called stage raising tweets, has generally gone away since the newest generation of Digital Signal Processors came out a few years ago.
previously, doing kicks, minimizing Path Length Differential was crucial to getting a good center image, but often resulted in rainbowing of the stage, to compenstate, a set of tweets, as you described, was often used in the A pillars, crossed very high (i have done 10k or even 15k) to raise the two sides of the stage.
however, with the advent of the good dsps with time alignment, it is not perfectly possible to do lower door or kick mounted midbass with dash mounted midrange and or tweets, and still result in a perfect on center image (for the driver). and that is why to me, its very important to aim the tweets properly.
the only people, in the compeittion scene at least, that still run secondary tweets, are generally those using HLCDs or going for SQC2 seater class, though of course, there are notable exceptions.
but i would think that most people where, when they want pillar pods, they would be talking about using them as the location for their primary tweeters?
in either case, aside from shipping and aiming reasons, the other thing baout doing apillar tweets, is that in order to best utlize it, IMO its best to have some form of DSP avaible and actively power the entire thing. when you have a wide separation of tweeter and mid, and running it just passive, you leave a lot to chance as to how the overall system will sound.