C560 PLT INBOUND TO SNA IS QUESTIONED BY ATC REGARDING SPD BELOW LAX CLASS B AIRSPACE.

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FO WAS FLYING. WE HAD BEEN ASKED TO KEEP OUR SPD UP AND WERE BEING VECTORED OFF OF A STAR INTO SNA. THE CTLRS TURNED US S AND THEN E DURING THE DSCNT. WE WERE WELL S AND I THOUGHT E OF THE CLASS B AIRSPACE WHEN WE DSNDED THROUGH THE FLOOR ALT OF THE CLASS B. THE CTLR THEN TURNED US BACK N AFTER A FEW MINS. THE CTLR ASKED OUR AIRSPD. I REPLIED '240 KTS; WHAT DO YOU NEED?' THE CTLR'S REPLY WAS 'I DON'T NEED ANYTHING; BUT THE FAA NEEDS YOU AT 200 KTS.' I SAID 'I'M SORRY. I THOUGHT I WAS FAR ENOUGH E TO BE OUTSIDE THE AIRSPACE.' THE CTLR'S REPLY WAS THAT THE BOUNDARY WAS 5 MI FURTHER E. THE CTLR HAD VECTORED US BACK UNDER THE BOTTOM CORNER OF THE CLASS B. FACTORS: ALL THESE CLASS B AIRSPACES ARE EXTREMELY HARD TO DETERMINE BOUNDARIES WHILE AIRBORNE. THERE'S NOT THE NICE ROUND; UPSIDE-DOWN WEDDING CAKE LIKE THEY SHOW IN THE BOOKS -- THEY'RE FULL OF SQUARE CORNERS AND CURVES THAT DON'T MATCH UP WITH ANY NAVAID. CTLRS SHOULD BE REQUIRED TO TELL YOU 'YOU ARE DSNDING UNDER CLASS B' OR 'CLR OF CLASS B.' AFTER ALL; IT'S RIGHT IN FRONT OF THEM AND THEY'RE LOOKING AT IT; AND THEY CAN SEE WHERE THEY HAVE YOU HEADED. IN A HIGH TFC; HIGH WORKLOAD ENVIRONMENT WHERE MOST OF THE CLASS B IS LOCATED; IT'S NOT SAFE; NOR DO YOU HAVE THE TIME; TO CONSTANTLY PLOT 2 XING RADIALS TO SEE IF YOU'RE IN OR UNDER A CLASS B. SUPPLEMENTAL INFO FROM ACN 618281: THE FLOOR OF THE CLASS B IS 7000 FT MSL AT THAT POINT. WE THOUGHT WE WERE E OF THE CLASS B AIRSPACE AND DID NOT REALIZE WE WERE UNDER IT. WE HAD REFED THE CLASS B CHART AND DECIDED WE WERE OK TO GO 250 KTS. THE CHART WE WERE USING IS DIFFICULT TO PINPOINT POS ON. OUR POS WAS IN THE VERY SE CORNER OF THE AIRSPACE. IN RETROSPECT; WE SHOULD HAVE BEEN CONSERVATIVE AND SLOWED TO 200 KTS.