I've noticed the same break points being problematic.
For example, a 1,990 ship:
- cannot be targeted by spinal mounts but a 2,000 ship can be.:
- at less of DM disadvantage in being targeted by attack rolls
- less of a signature DM to being detected with sensors.
A 2,000 to ship is not immune to turret crits but a 2,001+ is immune.
Basically, you're better off with any ship size greater than 2,000 or less than 2,000. The 5,000 ton ships have a similar set of weakness.
The 1980 HG has some useful language regarding ship size and tonnage codes that could be useful in handling these break points " Hull tonnage for both metal hulls and planetoids is expressed as a code given on the tonnage table. Each specific tonnage level includes all values between it and the next highest stated level. Thus, tonnage code A includes all tonnages from 1,000 to 1,999 tons.
It seems like the break points in advantages and disadvantages should be linked in similiar patterns without leaving these two specific sizes as the worst of both worlds.