form flr fp requirements

[daifer89]

i am a british citizen and my partner is from the caribbean he applied for extension using form flr fp as we do not meet the financial requirement for form flr m. we have been together 9 years and now have 3 children together. we are not married as yet but we are in a commited relationship and will be getting married in the next 2 years. he works full time and i am a univerity student and i also work part time. our wages combined are £16500 which is less than the amount they request. we submitted form flr fp on the 13th march 2017 and he received acknowledgement and biometric enrollment letter on 28th march 2017. he enrolled biometric on 29th march, however i have now been informed that we would be exempt from the £18500 financial requirement as i am in receipt of disability living allowance for our first child who is special needs, and instead would only be required to prove adequate maintenance. my question is do i need to ring home office to query this to have the form changed from flr fp to flr m, or would they notice that we qualify for flr m and grant him leave on that grounds instead whilst going through the application as i had submitted documents which prove i receive the disability allowance benefit. are they able to grant you leave under grounds you qualify even though you didnt apply for it? or would they go ahead and grant leave via flr fp because thats what we applied for, then we would have to resubmit flr m form and do a switch? need some advice please as i am unsure of how this works.