Air filters which are hard to access are rarely changed as often as necessary. We frequently see HVAC systems designed by someone who obviously has never had to service them.
Placement of filters and air handler access doors in very hard-to-access locations such as at the far end of a minuscule attic behind a forest of trusses means that the system is very unlikely to receive the periodic inspection and maintenance it needs.
We prefer to see A/C filters placed at the building side of the air return register or grille, so as to protect the return duct from debris accumulation. The more common filter placement on many systems is right at or in the air handler.