As it stands, players can defeat enemies while taking almost no damage.

Currently, players can lure enemies toward land within an area and defeat them while taking almost no damage.
Is there any way to address this?

To start, I will try setting the IdleRadius to be smaller than the TerritoryRadius and see what happens.

Hey, IdleRadius won't help here. It only controls when the leviathan despawns with nobody around. Right now the best fix is in the config:
- FlameReach up to 40 and LungeReach / BiteReach higher, so it reaches further onto the beach
- ShoreReach and ShoreMaxHeight higher, so it goes after players standing further up the shore
- BodyDamage lower and FlameDamagePerSecond / BiteDamage higher, so kiting it from land takes longer and hurts more

A proper counter to beach kiting (something like a ranged attack or diving away when hit from out of reach) is noted for a next update, thanks for the report.

I had mistakenly thought that IdleRadius defined the range within which movement is permitted—I assumed that setting it to a value smaller than TerritoryRadius would keep the leviathan from leaving the area.
Understood. I will review the settings you provided and make some adjustments.