Happy Wanderer,At 4000' you should probably be on a Flight level as you are above the transition altitude.If lower (below 3000') and you decide to penetrate the MATZ, the sensible thing would be to contact the operator of that MATZ and fly in accordance with their instructions. If possible you should remain on the RPS, and this should be the norm unless they require you to set the QFE to ensure separation aginst traffic within the MATZ. Once you are clear of the MATZ, RPS should once again be set.