Maintained Schools receive their Sixth Form Funding from the local authority along with their Schools Block funding, whilst non Maintained Schools, colleges and 16-19 education providers receive their annual funding allocations directly from the Education and Skills Funding Agency (ESFA).
Guidance on the 16 to 19 funding formula for the 2018-19 academic year, including a presentation on the funding rates and formula can be found on the gov.uk site.