Sieging a POB really takes long time even with more than 5 Battleship, so I have an idea
How about adding a Siege Slot for Battleships;
1 Siege Slot for Light Battleships and Medium Battleships
2 Siege Slot for Heavy Battleships
Siege Cannon can be mounted to only Siege Slot
(optional)Siege Cannon should have ammo capacity (200 or 300 Ammo Capacity)
(optional)Siege Cannon ammo price will be very high ($50.000 for each 200x50k=10M)
(optional)Siege Cannon ammo only manufactured at POBs and POBs will sell them
Siege Turret will have 0 degree firing arc (no arc), so cannot be used in Combat (or is it possible to make them only effective vs POB with FL hook?)
Siege Cannon should have very very slow projectile speed (200 or 300ms), but 5 second reload so you can fire 8 or 10 projectile before first one hits the POB
Siege Cannon should do massive damage (more than 3M damage)
Siege Cannon should have 6K RANGE.
(optional)Siege Cannon should use Ballistic Ammo so they don't require any Energy requirement to fire.
About POB Defences;
How about adding different POB Defences like;
Light Defence Platform (Effective vs Snubs/Gunboats)
-25M Armor Points
-20Min Respawn time
-10x Battleship Solaris Turret
-8x Battleship Solaris Gattling Turret
Medium Defence Platform (Effective vs Gunboats/Cruisers)
-50M Armor Points
-35Min Respawn Time
-10x Basic Cruiser Primary Turret
-5x Cerberus Cruiser Turret
-1x Light Mortar
Heavy Defence Platform (Effective vs Capital Ships)
-75M Armor Points
-50Min Respawn Time
-2x Heavy Mortar
-4x Mortar
All Platforms should have same size with Battlecruisers (IMG BC) their Turrets cannot be destroyed and New Models for PoB Defence Platforms