The ever increasing quest for smaller details on computer chips requires increasingly accurate lithographic machinery. This paper discusses part of the design of a permanent magnet based vibration isolation system to be used within such machinery. In such system, the passive permanent magnets provide the gravity compensation and active electromagnets the accurate positioning. Flux-focusing materials may be incorporated for structural support, flux focusing and magnetic shielding. This paper investigates the feasibility of analytical surface charge modeling combined with the method of images for accurate force prediction in a suspension system with soft magnetic materials. More specifically, it is researched to what extent finite support lengths reduce the analytical model accuracy.