They don't spread the cost, you carry on paying until the cap is reached however long that may take.
By 2016 everybody, including self funders, receiving care should have had a personal budget against which all their care costs, calculated at LA assessed rates, were recorded and set against their lifetime cap.
EDIT
As I said previously studying the implications of the Care Act 2014 is largely academic, implementation of the sections on lifetime caps has been deferred until 2020 when there will be a new government. Nobody knows what the outcome will be.