Could you clarify what this means.
Is it signal sighting and using the DOO that is the problem. Or putting the question in a different way if they had full dispatch at all stations at all times would the issue go away? (Considering many can take 8 coach trains already)
I have no idea what the issues are in the GN (Although I suspect, if they are what I am thinking they will be mostly / wholly between Drayton Park and Moorgate.
The central seating position on class 700/717s presents two entirely separate but related issues.
Signal sighting: Each driving cab puts the driver in a different position in relation to the length of the train / being able to see the aspect of the signal. A driver in a class 313 is on the left side of the cab a few feet further back than the same driver in the middle of a longer 717 means that signal viewing can be drastically changed. Until you actually put a train there it's nigh on impossible to see exactly what you are up against.
There are restrictions in place at Kings Cross with departure of class 387 units requiring additional staff for this reason.
There are some restrictions still in place for the working of 700s at various locations, some that would surprise you for these reasons.
Adjusting signalling infrastructure is an incredibly expensive exercise and cannot be done overnight without design work, survey work and installation that is way beyond my understanding.
As for dispatch. Any station that requires manual dispatch presents it's own unique issues. Station staff variably dispatch by bat which has to be displayed to the driver either at the cab door or directly in line of sight through the windscreen. The length of stock again plays an important part in how this achieved and this is of course over and above the "RA" methods used elsewhere.
The number of stations that rely on manual dispatch are dropping all the time as the on board cameras of 700s / 717s are used. But that is only when lighting levels are at genuinely acceptable levels 24/7 to allow the cameras to be seen correctly.