Hi Claire and welcome to the forum
An insolvency practitoner who takes into account overtime as part of someone's regular wage is treading on thin ice.
Unless the overtime is guaranteed, which is quite unusual these days, it can be denied or withdrawn at any time. If this is the case, then your income may drop to a level where your IVA payments cannot be sustained, and then the IVA will be at risk from failure.
I much prefer to operate the 50% uplift ruling, where there may still be some incentive for you to work overtime, as you get to keep half!
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
View my IVA blog at:
http://melaniegiles.blogs.iva.co.uk