I don't agree with this high wing / blind time theory being banded about. A properly flown constant aspect circuit uses a very shallow bank angle, and since you're mostly either in a climbing or descending turn , the traffic in front is always more-or-less ahead, and above the coaming. With a rectangular circuit the Viz of traffic ahead is fine in the climbout, but non-existent in most high-coaming aircraft on finals. The wing is irrelevant where aircraft you could interfere with are concerned.
A genuinely tight circuit has to be constant-aspect, unless you are planning to use 60°+ bank in the circuit turns, which wouldn't be very clever. But, the airfields where people routinely fly circuits that require a chart, drive me up the wall, even if flying square circuits. Having said that, it's usually the fault of individual pilots, not the airfield itself.
At BDN we used to regularly mix everthing from a Vigilant to Tornado in the same circuit (23L usually), constant aspect, with heights and distances from the runway altered for each aircraft to maintain a constant circuit duration (about 5 minutes) and position. I don't recall it ever causing us a significant problem.
Also, a constant aspect approach is the only (in my opinion) sensible approach to flying a PFL. John Stewart-Smith's article on the subject in FSB sums it up without me going into it more. And if you're going to use it for a PFL, why not practice it at home!
G