The hull insurance is granted on an agreed value basis, which means that you agree, together with the insurer, the price of your aircraft.
Air Courtage Assurances recommends you to insure your aircraft for what it would cost if you had to replace it with an identical aircraft (Make, model and year) rather than considering the price you have paid for it.
Overinsuring the aircraft is not recommended as it will increase the price of your insurance premium, but under-insuring the aircraft could lead to an aircraft considered as a "total loss" while it could have been repaired!