The offer should be aiming to give the creditors as near as possible to what they signed up for -- so remaining payments, including the 12 months equity release. In your case this would be 48 X 272 ... so £13056. You are saving them 4 years of messing about with small dividend payments every few months, so could round it down a little. If it were my IVA I would try for £10k, may be ready to up to £12k, but this isn't an auction scenario, they won't appreciate you upping the offer in £500 increments.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
Please ensure when making your offer you are clear that unless the iva is concluded via this full and final offer you will not have access to this money for any other purpose.
Sharing from experiences of dealing with debt
There is a solution for everyone .... Just need to stay positive !