I know what your saying Scott but how much they will lend you and the % of deposit you need are two different things. I assume they looked at all your permitted income (some income is not accepted by some lenders, eg overtime that isnt guarunteed) then deducted whatever you pay out each month in commitments (utility bills, council tax, loans, credit cards etc) then multiplied it by whatever.
That only works out the max they will lend to you. Regardless of this amount they will ask for a set % as your contribuiton. In other words, they demand that you take a % of the risk. Its called the loan to value or LTV. So if you want £90k for a house valued at £100k (you put down a 10% deposit of £10k), it doesnt matter if they will lend you £200k, the LTV will remain the same. They will want you to put down 10%
Otherwise they'd be lending you all the money for your house (100% LTV) and all the risk would be on them. Thats precisely why 100%, 110% and 125% mortgages have been scrapped. Does that make sense pal? Good work qualifying for £200k by the way!!!