I visited hundreds of Hidley's studios during the '70s and the only one to
really impress me was the Phonogram complex in Hilversum, The Netherlands.
And I believe we addressed and conquered those specific issues in the "Westlake" design with which I found fault. The Fostex Laboratory Series monitors exhibited extremely well-mannered dispersion and integral time correction/phase alignment. They did not sound "harsh". And I dare say that no-one who heard them would disagree!
IMHO.
BTW, in order to provide a correct low-frequency acoustic load for the monitors, we supplied both half-space 2
π steradian soffit mounting kits and vertical versions with plinths for full-space 4
π steradian environments.