Let me get this straight, you are now flying from LPL that has a route from MAN, and closer, purely because you had to walk outside?!
Firstly, as you said, MAN is closer and better connected to public transport (MAN has a rail, coach and bus station) and if I remember correctly, public transport to LPL still stops outside in the open air and is a slightly further walk to the aircraft from the gate at LPL too (granted not by a huge amount but still)
Seems like your splitting a rather fine hair to me!!