Oh dear Jet A1, the old chestnut of charter seat config again. I suggest next time you are parked next to a Monarch aircraft downroute, you leap out of your shiny GB jet with a tape measure and actually measure the seat pitch!
And where exactly are these "middle of the night" flights? The latest I can find for the middle of August is a 15.55 departure compared with GB's offering of flying via LGW departing MAN at 16.15 and arriving into ALC at 23.55. That's nearly 8 hours! The return flight leaves ALC at 00.40 and you eventually arrive back into MAN at 07.40 (Check yourself, going out on 14th August and returning on 25th August),
Now prices, Monarch not cheap admittedly at £193.85 but GB takes the biscuit at £269.00.
I know which airline I would fly with!