I think the problem is more along the lines of finding a justification that can be consistent while not forcing capitals to spend the entire game a billion kilometers from the nearest body of importance. IIRC, cruisers are intended to be platforms to bombard other capitals and structures: I don't know if the intent is to include planetary fixtures, but if so the cruisers will have to have some way of getting within range. If you base it on gravitational effects, Jupiter's gravitational pull is 1g at ~110,000 km. If we assume capitals are not intended to get lower than an earth-equivalent LEO, that means capital ships could never approach a Jupiter-mass body closer than that distance. Continuing to use Jupiter as a reference, that would put all four of its major moons within capital territory.
From a purely "g" related view, this would seem to be viable for Earth-mass bodies and greater. Of course, this presents a few issues: given that gravity and acceleration are indistinguishable, either the ships cannot accelerate faster than 0.9g (and we cannot use artificial gravity to dampen the effects in the room) or we can use artificial gravity to dampen the effects of acceleration (and we can then use that technology to allow us to approach the planet).
You mention tidal forces as a potential limiter, but then a similar issue arises based on rotation. If an object rotates fast enough, the difference in "centripetal forces" across the diameter of the warp drive is no different from the tidal forces of a dense object. This also creates an issue regarding the approach of objects with no significant tidal forces.
