I simply cannot get my mind around how the arithmetic works for short haul, but then again I'm not aware if short haul flights can get delayed at LHR in quite the same way that long haul ones apparently can be.
ATC don't discriminate, SH or LH will get the same delay, whatever it happens to be when they arrive.
The only, perhaps avoidable, penalty LH get is when they pitch up before the end of the night jet ban, are not exempt and so and have to wait till 06.02 before landing. It's not unusual to have traffic arriving from 05.30 and then holding for 20 to 25 minutes.
Given the number of a/c that can land before 06.00 it's nothing more than a political sop that makes us continue with the 06.00 restriction. The 06.00 to 07.00 hour is then needlessly busy with lost of crossing tracks on base/final approach with knackered pilots and atcos working their socks off as ATC try to get back to no delays for the start of the 07.00 to 08.00 hour. Totally stupid imo.
Note: individual a/c of any type may, at any time, move slightly up or down the queue inbound as ATC look for the most efficient landing order down the approach, but time gained or lost is only a few minutes.