a contribution to the range issue:
some games ago, I took some serious beating from ai PJIs and decided to try them out. now, what suprised me most was the massive range of these things, they have like 31.500 range. enough to cover a grav well to about 70%, even more for smaller ones. so, to get a bit of perspective, when you do a game where you want to play around with the new things, maybe take the time to research them and build one of them just to see what a range of 30.000 + looks like.
now, based on that I'd say the absolute maximum range of SBs should be lower, but not horribly much so, IF that is the only thing that changes. there are other ways to stop the bypassing (or at least making it more difficult), but I'd say if the range, and nothing else, changes, then the following would be good.
20.000 - 25.000 long range weapons, thus only a portion of its firepower has the massive range and can truly harass ships almost everywhere in the grav well.
~ 15.000 mid range weapons. still long range, but can be avoided without dramatic effort.
less than 5.000 - 10.000: close range weapons. those things should really just kick in for closer bypassers or against a force that decides to directly assault a SB.
the anti structure units (ogrev, adjunctator) should outrange mid-, but not long range weapons. why? well, a SB in its full military equipment is a big investment and not even a direct counter should be able to take it down without any losses whatsoever. if you look at the units' damage, they'll probably finish it off without too much losses if only a third of the SB's firepower is directed at it.
once again, this is only about the range issue and if it is thus changed, of course there should be a rise in cost to accomodate for the increase in usefulness. if other things are used, such as general moving SBs, range increases via buiable upgrades, etc., then the increases do not and probably should not be as dramatic. maybe I'm even all wrong, but with what I suggested, I'd say we could have a structure that can guard an area on its own against modest resistance without becoming utterly unbypassable and indestructable. in other words, a struture that fullfills a clear purpose and is useful in a different way than just a bunch of turrets.