If you have your payments reduced and an extension added, then any extra you are able to make now will simply increase the money to creditors. It would be better not to have the reduction, IF you are comfortable making payments at the current level. However, in difficult months it would be difficult to reduce payments temporarily.
That said, and according to how your proposal is worded, and how your IP is minded, he should have the discretion to reduce payments by up to 15% without extending, unless you have a guaranteed minimum dividend to meet.
Who are you with ?
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014