What you have to bear in mind is that the existing signals were there to protect the junction. Now the junction has moved to the north end of the station there is now no need to have the signals on the end of the platform as today. All the scenarios have been gone through with regard to the position of all the signals in the new layout for all proposed train movements from about 4 miles north of Market Harborough to approximately the same distance towards Kettering. Full signal sighting carried out and full risk assessments completed under the requirement for scheme plan approval.
An earlier version of the Leicester MAS scheme envisaged both the rebuilding of the station and the reversion to the original Midland alignment at Great Bowden, and in this the pair of crossovers were to be north of the new station and for 50 mph. In the final version it was still hoped up to a very late stage to do all the realignment works, but the crossovers were moved on to the curve south of the station (and the signals were moved appropriately) so as not to complicate that realignment work if and when it happened. The crossovers that were put in were for 40 mph, which had become pretty much the standard for the modernisation of the London to Trent line. But if my memory serves me rightly, whereas none of the original junctions between running lines in the West Hampstead scheme got flashing yellows, several in the Leicester area did.
What you say about 25 mph crossovers for Market Harborough is very disappointing. Is this another bit of de-speccing of a scheme outside the South-East, or are we seeing a reversion to the old London Midland Region love of low-speed crossovers with highly-restrictive approach control. 40 seemed a very good compromise in the Leicester area for effective use of the reversible signalling: Sunday trains seemed to be able to use the facilities very smoothly (and quickly accelerate back up to line-speed, not the SIMBIDS 80). I note that the replacement Wellingborough north junction is only for 25, although I recall reading somewhere that this is where most down trains for Corby will cross fast to slow. Will the new Wellingborough south junction be equally slow?