From the .gov website:
The Valuation Office Agency Rent Officers determines Local Housing Allowance (LHA) rates used to calculate housing benefit for tenants renting from private landlords.
LHA rates are based on private market rents being paid by tenants in the broad rental market area (BRMA). This is the area within which a person might reasonably be expected to live.
Local Housing Allowance rates
LHA rates are based on rents, and limited by legislation. These rents are being paid by people with the same number of bedrooms as the property where you live, or the number of rooms you and your household needs.
You can check the LHA rates for you, based on the area you live in.
You can also check how many bedrooms you may be eligible for, based on the number of people in your household.
So nothing to do with the size of your home.
Which is as it should be. But the OP wasn't talking about the part of the benefit which covers your licence, they were talking about the part of the benefit which covers your mooring cost.