I think it's one of those questions that needs to be asked inversely: "Is there any IRS publication or reference that I can use to confirm that the cash value should NOT [my emphasis] be included in the RMD calculation?"
The answer is "no." Can't think of any reason at all to exclude that.
A mid-year amendment to the match formula is prohibited under 1.401(k)-3(e)(1). The modifications to that rule in Notice 2016-16 provide that the only mid-year formula changes allowed are ones made with at least 3 months remaining in the year and that increase the safe harbor contribution. See Section D of the notice. The amendment under discussion would result in lower SH amounts for at least some individuals. So, if they do the amendment mid-year, they would fall under the rules for reducing or suspending the SH contribution under 1.401(k)-3(g) and lose the SH for the year.
you are correct, you are not supposed to change things after plan year end.
I agree with your calc that 1/12 of 265,000 = 22,083.33
unless you are talking about schedule C income, then 25% of that is 5520.83 for deductibility. deferrals do not count toward deductibility, so that would be 5520.83 in profit sharing