The calculated bearing of the Mitre Square site relative to St. Paul's dome is 90.67 degrees, and the calculated bearing of the former Dutfield's Yard, where Elizabeth Stride's body was found (the Henriques Street location) is 90.40 degrees. I had figured that these lines would be at precisely 90 degrees, and knowing that they could have been made precisely 90 degrees if the designers had intended, I was puzzled over the "error." One of the apparent purposes of these sites was to "point" to St. Paul's, and to serve as a visual "horizontal" reference - a hint that there is some significance to bearings of Ripper locations relative to St. Paul's. The slight "error" does not detract from these purposes, but it apparently was intended to send another message.
So, I looked at the usual suspects - Moon phase, dates with corresponding sunrises, etc., and the sunrise angle seems to have been the one intended. The corresponding date is 9/24/88, when the sunrise takes place at -0.54 degree, which is within 0.005 degree of the average of the aforementioned angles. Because of the precision with which angles could be measured even then, I assume that it was known that the sunrise occurred at this angle on this date. Note that the date is 9/24, i.e. 9-6. The angle is -0.54 degrees below the east-west axis, and the digits of this angle sum up to 9. So, between the date and the corresponding angle, there are two 9's and one 6. When the 9's are rotated, they become 6's, and the intended message appears to have been 666, as usual.
Note the angle to the Clarke's Yard site (Rose Mylett) is precisely 96 degrees, and 15 degrees to Ada Wilson's attack-site on Maidman/Wentworth Mews. When the digits of 15 are added together, the result is 6, and when combined with the 9 and the 6 in the bearing of the Rose Mylett site, the result is again 666 when the 9 is rotated.
So, the fact that these angles appear to have been intended to send clues in the form of "666" tends to support my theory that the angles to Mitre and Henriques were also intended to send this hint of a diabolical agenda, as indicated above.