It is all a bit odd... The Lancastrian's main power base was Yorkshire, Northumberland and Cumbria, while the first Duke of York's main holdings were in Shropshire and the Welsh Marches. The Duke of Exeter's lands were mainly in the North-East too. Only the Earls of Devon, Warwick and the Duke of Somerset seem to have had vast estates in the areas they drew their titles from. Kent, Essex, East Anglia and London were strongly Yorkist due to the concentration of nobles around there (the Bourchiers, Fitzalans and Mowbrays etc).