Fair share of freehold insurance bill?

Hi, I own (through my limited company) a 1st and second floor 3 bedroom flat which is a rental property in a Victorian house which is share of freehold. I own 2/3 of the freehold and the owner occupier who lives on the ground floor downstairs owns 1/3 of the share of freehold.

Traditionally, I have always paid the insurance and billed him 1/3 of this. My deeds say that I should pay 2/3 of any maintenance.

However, I believe that the insurance should be split equally. Or based on square footage.

The owner downstairs has just completed an extension and we are now facing a higher premium. I am sure it would be fairer to pay the building’s insurance based on our square footage or split the bill, alternatively possibly we could each pay our own buildings insurance going forward.

I am wondering if anyone can give me any advice?

Thank you,

David