The odd part of that is if you gave the person who made $200 a $50 contribution (25% of $200 in case it isn't obvious) you would have plan that meets the discrimination rules and no one would ever say otherwise. Everyone got 25% of compensation after all. .
Yet this person is $150 worse off then the allocation that supposedly violates the rules.
Hello we are from the government and we are here to help you-- strikes again!
Any reasonable and consistent method will do. However this is the accountant/tax advisor call. See previous discussion here: http://benefitslink.com/boards/index.php/topic/55122-allocation-of-contribution