But I did talk to one of the air traffickers about the show day itself. Apparently the average cloudbase was 800' and often down to 250' - way below the 1000' minima. The so called "clearance gaps" were more like "suckers gaps" as the Reds found out.
The Reds were just unlucky with the timing and did at least make an attempt.
But throughout the day there were extensive periods of satisfactory cloudbase, certainly not suckers gaps as you describe them, which were unused because of an unwillingness by the organisers to bring forward displays to fill the gaps left by known cancellations. Had XH558 been rescheduled earlier as soon as it was realised there would be gaps then its hydraulic glitch could have been sorted before the weather finally clamped at the end of the show.