[Suicide Junkie]

More like blocking all avenues of approach...

Which is why I highly encourage the use of leaky minefields!
Step 1: Remove minesweepers!
Step 2: Reduce mine warhead damage.
Step 3: Limit mines to 10 per sector!

Now, mines will have to be spread around in many sectors. Any single invasion force will miss most of the mines, but they will hit some, and those *will* do damage. Light damage for each sector, but some damage nonetheless. The ships will have to slow down for repairs, or suffer ever-accumulating damage.
The defender will quickly fill the warppoint sector, and then have to decide which paths to mine... lots on the path to likely targets, or spread them around thinly to catch the sneaky fleets that try to second-guess your mine placement.