This is exactly the kind of reason why 720s be refurbed to StanEx standards to overcome the shortage of 745s, as some posters suggest on other threads, is not a good idea! The distribution of passenger loads along these trains have to be carefully managed, and 2x 5-car 720's coupled together don't provide a gangway for passengers to move along the entire length once on-board. This obviously won't be fixed regardless of how you may fit out the interiors to make it more suitable for airport traffic. A pair of 720 would also be a capacity cut vs a 745 if reconfigured to a similar seating layout. That may not be such an issue now, but the 745's are futureproofed in terms of the capacity provided on the StanEx to accommodate the forecasted growth in airport traffic. Since there's no ability to add additional services to/from Stansted, due the single-tunnel approach and platform constraints, this needs to be protected.
I diverge slightly, so back on the original topic, the problem is at Liverpool St where passengers board on the nearest coaches to the ticket barriers (ie the back of the train), most oblivious to the fact when they get to Stansted, the front carriages are the optimal ones to be in (you get a few savvy customers who realise this, but most don't). Therefore at Tottenham Hale they have to direct people towards the front in order to prevent delays. The 720's only exacerbate this as the freedom to move along the train once in, is lost.
A 745 from Stansted is less of an issue, because unlike on the northbounds from London, there is no major boarding point en-route as most people in TOM are alighting. There's a bit of passenger churn through BIS/HWN but that's about it. If people board at the back in Stansted, the mid and front sections will naturally begin to fill at either BIS/HWN as people joining there can simply move along to available seats once on-board. A 720 however is a different story. Due to platform layouts in BIS and HWN, people will favour the mid-rear section and if that all gets filled in Stansted, they have no way to move toward to the empty front section once onboard. As the 720's are not the norm for StanEx services, you're unlikely to have staff in BIS/HWN managing crowd control like you do in TOM routinely. There's also simply not the same crowding there. As such, they have to ensure passengers are not filling the rear section in Stansted, so these seats are readily available for these other station calls.
Commuters tend to spread out and are not shy about sitting next to others or getting them to shift any bags off seats.
