Under the Schiphol TMA, 1000'-1200' MSL (which is actually a few feet more AGL). En-route cruise outside that, typically 3000-3500' or so. Over water, as high as possible - which is FL45-FL65 or thereabouts over the Channel/North Sea. Aerobatics, typically a block between 3000' and FL55, lower when practicing for a competition.
if C starts at 2500 i am at 2499.
LVNL (the Dutch NATS) advises us not to do that consistently. Around here they vector traffic for final approach at 2000' (Schiphol TMA starts at 1500') and wake turbulence is known to descend up to 700'. So their advice is to stay 200-300' under the base of CAS. Makes sense, also from the CAS bust point of view.