Hi acsn and welcome to the forum
Your IP will definately set the one off against the other, and well done for being able to make these increases to cover your higher mortgage payments. I do not feel that you need to tell them now, providing you are able to maintain your IVA payments, but quick e-mail would not do any harm just to put them in the picture.
I am sure that they will not require bank statements - I certainly don't ask for these unless I want to query something specific.
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