There is no need to measure anything to determine where the right side of the triangle goes, since it connects the points of the pentagram on both sides. This image shows that the triangle does not point to the CB and that the section of Penn Ave between the WH and CB is about 3 degrees off from the northwest section of that.
"I'm also willing to accept that two the four 23.5 degree avenues - especially the one you bring attention to - are slightly out from this angle. However, because the overall pattern of these four avenues leading off from the White House is symetrical with two of these avenues being 23.5 degrees exactly, I would say that the two 'slightly innacurate' avenues were also meant to be to at this angle or are making a reference to the angle of 23.5 degrees to complete the picture of the GP hiding within the map."
Please consider this image, The CB is offset to the north from the straight line formed by the northwest section of Penn Ave. There is no way in the world that you can assert that the middle section of that was intended to be or refrence 23 degrees.
"Overall I don't see the point in arguing about, or getting lost in 'slightly innacurate' measurements on a map covering several miles here."
Who is lost?? Not me. 3 degrees- slightly innacurate? Not to surveyors. I believe what you are saying is that you are really not that interested in the details and accuracy.
You might want to look at these five pages: