Not wsihing to be or sound pedantic, officlally, geographically, and by government administrative definition (but not in ECML or WCML railway terms), Northamptonshire, Lincolnshire, Nottinghamshire, Derbyshire and Leicestershire all all East Midlands, whereas Staffordshire, Warwickshire, Shropshire, Worcestershire, Herefordshire and the old West Midlands Metropolitan area are all West Midlands.
To add to the confusion, the unitary authority authorities of North Lincolnshire (Scunthorpe and surrounds) and North East Lincolnshire (Grimsby and Cleethorpes) are NOT part of present day Lincolnshire and therefore NOT in the East Midlands but are 'up North'.
Therefore, officlally, many parts of the Midlands are further north than places which are 'up north' proper and vice versa. This will not necessarily coincide with the perceptions of people who live in those borderline areas between 'Midlands' and 'North' as to whether they consider themselves to be 'Midlanders' or 'Northerners'. Places like Retford, Worksop, Glossop, Buxton, Stoke on Trent, Newcastle under Lyme, Chesterfield etc all spring to mind, all in the Midlands but their next nearest major regional city not being so. Accents, TV channels, which major regional centre they look towards for work, retail etc will all influence or distort that self or others perception of regional identity or affiliation one way or the other.
The same applies between the Midlands and the South. Banbury is in the 'South East' because it is in Oxfordshire whereas Kings Sutton, a few miles south of Banbury, is in the 'East Midlands' because it is in Northamptonshire.
Hope that clears that up.