CoG Centre of Gravity

By that method a true delta would put the suggested CofG at 50% root chord?

A pure triangle delta would be tricky, with a zero chord at the tips.
An Ogival (Concorde or Vulcan) - that's about right - don't forget there is effectively no lift at the root, because of fuselage interference.
An SR71 - well - suck it and see! You have to take into account the lifting body, and most of the wing is engines!
-
I don't claim it's a 'fits all sizes' solution, but it gives a fairly safe start-point.

"there is effectively no lift at the root"
I think it would be more accurate to say there is less lift at the root.
At a positive angle of attack almost any shape produces some lift albeit at the cost of high(er) drag.