StratOps, I don't have a page reference offhand. Surface-to-surface shots are still a form of orbital bombardment(don't ask me), and ortillery shots get a -2 to-hit if the target hex is TAGged. This isn't as suicidal as you think, as the -4 mod for TAGging an immobile target(a hex) means the TAGger can do this from the limits of the TAG's range, and thus outside the blast radius of a capital strike(if it hits, or doesn't drift too much, which the TAG also helps with). Also, I believe capmissiles also gain an additional -2 for ortillery shots compared to other guns, so you can reasonably expect to hit things dead on with TAG-guided capital/subcap missiles.
On a side note, if a PWS is flying at any Low Altitude and fires capmissiles at the ground, it's treated as an orbit-to-surface shot, but without all those pesky atmospheric hex modifiers. Combine that with a TAG, and a Leopard-PWS or hovering Mule-Q can reasonably expect auto-hits with capital-scale guns if you're willing to brave interceptors and possibly ground-based AA. >:D