So, if grav well control is supposed to be what entrenchment is fixing, then we need some actual grav well controlling units.  Frankly, entrenchment wouldn't have even been needed if we'd still had the mark one phase disruptors from beta that prevented phase jumping instead of just slowing it.  I know I had plenty of pitched battles with that to keep my grav wells from just being stepping stones.  Admittedly it was a bit of pain if you got trapped by one, but that was the whole point, force your enemy to scout out your position before jumping his/her entire battlefleet in, and if they still did, you had a little time to get your fleets in a position to respond. 

So my suggestion for Sins is to add the original phase disruptors ability to the starbases with a few minor changes.  And yes I know we went through this several times in SOASE beta.  The changes to the ability would be as follows:

1.  preventing phase jumps would be a researchable, upgradeable ability for starases

2. the ability would have a per second/minute antimatter cost.

          This would prevent a lone starbase from stopping a fleet in its tracks permanently and allow the possibility of retreat, albeit a retreat that would probably cost a lot for the attacker.

In order for this to work though, some other changes to the starbases would be required, such as greatly increasing their weapons range.  We are talking about an enormously expensive, super-capital ship sized installation whose sole purpose is supposed to be grav well control, its current weapons range of less than a cap ships is just ludicrous.  There are several ways in which this could be done.

1. The simplist way to increase the starbase's range is to simply increase the range of its weapons.

2. The more complicated way is to allow starbases a certain number of tactical slots with which to build additional grav well defenses.  the number of tactical slots would be sharply limited, and the tactical build options should be different from a planet's.  Say minor starbases instead of gauss cannons and hangers, these minor starbases would be about the size of 2-3 hangar bays and would have 2-4 upgrade slots with which to arm them.

3. A combination of the two, with a longer range starbase and some tactical slots for shorter range, specialized defenses.