Another idea for an ability that just occurred to me:
Blockade. Activate this and your fleet formation spreads out while the circle surrounding it grows. Depending on your fleet size, it can grow enough to cover an entire planet, wormhole terminus or similar objects of strategic importance. Of course you can now engage every fleet that wants to pass through.
Your fleet is unable to move though, and the supply consumption is increased to to the logistic challenge of coordinating over bigger distances.
Since your fleet is dispersed, you get a penalty in the deployment mechanics if it comes to a fight. Maybe some kind of time delay in getting deployment points.
I thought this might add nicely to the blogpost idea of watching for targets along frequently used routes instead of chasing them around.