It's not clear from what he said today, but I'd be surprised if their isn't some kind of marginal relief - i.e. Step 1: the liability is calculated based on a figure of 200k and that is the amount of top slicing relief to be given, and then Step 2: the actual taxable lump sum is put into the assessment and tax calculated accordingly, but the top slicing relief as per step 1 is what is applied.
That is a simple, fair and straightforward way to do it and it only took me 30 seconds to figure it out, so hopefully the guys getting the big bucks managed it!