bigjim - you're idea would only really work with the GLA route, and that makes the suggestion unviable.
GLA has as far as I'm aware been persistently poor, whereas MAN has been erratic with some flights virtually full and others almost empty. As an extreme example last week one flight was upgraded to an E195 and had 100+ on board ahead of Spurs v Man U.
The average for RNS and GRQ on an AT4 would be nothing like mid-40s because the capacity cap means you would lose pax on flights where current loads exceed 48. The AT7 works just fine, likewise for MAN because a number of individual flights have had loads in the 50s and 60s, but I accept for the latter they need greater consistency and to get the overall average up. To be fair RNS and GRQ had similar averages in the early days and they've now grown, hopefully MAN will do the same but we'll see.