Commercial loading on shop insurance

Hello I am looking for some advice as I am very confused with this situation

I have a 15 year lease on a small shop, the building consist of 2 flats and a shop
My landlord rents out the 2 flats to tenants and I have just the shop.

When the building insurance is due the landlord states that my contribution is 58%

I asked the landlord why I have to pay 58% of the insurance and the landlord stated that its due to commercial loading applied to the policy due to it being a business

I have asked the landlord to provide me with a letter from the insurance company stating how much of the policy has commercial loading, but the landlord refuses to provide me with this?

As there are to flats and my shop I would have said I should pay a third of the policy?

I have spoken to the landlord again on this matter and now they say its was worked out on the floor space but when I pointed out that the flats have more floor space than the shop the landlord cant really answer the question and I feel like I am being ripped off . from a £800 policy I am paying 58% for one small shop yet one flat is 2 floors high any advice welcome