There is no specific answer we can provide that will meet your needs 100% without knowing how the EQ response of your room behaves, a completely balanced room will give you the best answer for where to place your monitors. Going through the process to properly balance your room will give you the best placement for your speakers, and give you the best sound for your mix.
Room balancing is an art unto itself and as most rooms change frequently, as in bedroom and project studios, the distance is subjective.
Please review this Speaker guide we put together that is available on the MTM Speaker Download Page. It goes over speaker placement, distance and other considerations.