Will a participant satify their Minimum Required Distribution if they withdraw the required amount from one source (segregated account) within their 401(k) plan? Given a plan has after tax contributions, you can see where participants could minimize their tax liability by withdrawing from just the after tax money. Would the 72 regs affect the proportion of the after tax withdrawal?

I think it is permissible (as well as desirable typically) for the minimum required distribution to be paid first from the after-tax employee contributions account. See IRS Letter Ruling 9840041. Especially considering I can only cite a letter ruling to support this viewpoint, you probably want to do other research to confirm this conclusion.