Hi tidar and welcome to the forum
Your IVA payments have presumably been set at an affordable level in conjunction between you and your IP - or more likely these days by creditor modification. Yes you do seem to be paying higher than average contributions, but presumably you earn a reasonable salary - and you have higher than average debts. The ceiling percentage of how much is paid in can be equated to 100% plus IP costs plus statutory interest at 8% per annum (if your proposal provides for this).
Windfalls can potentially shortern the period of an IVA, but only if you manage to achieve the 100% formula I have referred to above. Payments that you have already made will be deducted from this sum.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk