Were it ever thus? 20 years ago the MMR was far more expensive from Wellingborough to London than say Northampton to London. Our sons went to University in Loughborough or Nottingham and we always felt we were paying a premium to use the line.
This dates back to the boundary of the "London South East" area, later Network South East being set at Bedford with the consequence Wellingborough and Kettering ended up with much more expensive "Inter City" fares. Same situation existed at Ipswich