Hey, from the instructions and on-line materials BMS makes available, I understood that while they recommend to use all three spacers for most applications as I think they put it, you could do what you feel comfortable with. When I compared the stock part and the BMS, I decided there was such a difference that even installing with no spacers the BMS would be a world away from what came factory installed. So I started small and just kept adding until it "felt" right to me. YMMV.
2013 F30 335i 6MT M-Sport - Blk Saph. / Beige Lthr / Wood Tr. - Tech Pk - VSS M-Adp. Susp. M-Perf Stainless Exhaust M-Perf. brakes