When imputing income is imputed, what is the effect on a motion to vary or change support?

I add that once the court determines that it is necessary to impute income, the onus is on the party proposing a different amount on a motion to change (or a different approach to the calculation of income) to establish a material change in circumstances. In Galati v. Leach, 2018 ONCJ 315 (O.C.J.), O'Connell J. of the Ontario Court of Justice stated at para. 49 that it is well settled law that when, as here, "... income is imputed, then the issue will generally be res judicata on a motion to vary or change support... Although the court always has discretion with respect to the issue of res judicata and can consider fraud, fresh evidence, additional disclosure or issues of fairness, the principle of res judicata provides that generally, a matter cannot be re-litigated once it has been determined on its merits." [Citations omitted.]