Oops!
I made a little mistake in some of my previous comments. Those of you that are as perfectionistic as I am (and are doing your own coding) might want to make note of a minor adjustment...
Previously, I had noted that the DMG tables followed a "mirror image" multiplication pattern for all levels except 4 and 20. But that should really only include 4 as an exception. It turns out that the exact pattern for level 20
isn't actually listed in the DMG (or ELH) tables at all!
When we extend the DMG pattern for CRs > 20 and Levels >= 14, the DMG tells us to double the number from two CR levels below. This works fine for levels 14-19 because their multiplier patterns have already been correctly established by that time. However, when applying this doubling to level 20 we're actually creating an "erroneous" pattern (that matches only level 4 and the ELH).
Technically, either pattern could be used arbitrarily if following the table values only, as it doesn't list the one critical number (CR=21) needed to determine which was used. Therefore, I'd like to propose that it be formally extended by using the same pattern as the rest of the DMG table (except level 4), which was apparently the originally intended pattern of the developers, and not by using the "doubling rule" strictly as stated (which isn't strictly followed already elsewhere).
To do this, a single value must be reformulated. For Level=20, CR=21 should instead be 2.25 times the CR=19 value (also 1.5 times the CR=20 value) for a total of 9000 XP. Further values to the right of that (CR=23,25,27) will then be doubled correctly by using this number (instead of 8000) in their calculations.
Does anyone have any complaints about "standardizing" in this way?
