CRJ100 CREW TRIGGERS LOW ALT WARNING DURING LOC APCH TO RWY 22 AT LEX.

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ON APCH TO RWY 22 AT LEXINGTON; KY. FO WAS PLT AT CTLS. ACFT WAS LIGHT AT APPROX 40000 LBS WITH A SLOW REF SPD. ATC CLRED TO JOIN THE LOC; GS OUT OF SVC AT 3200 FT. WE CROSSED BRIDL WHEN NDB 090 DEGS TO 270 DEG NEEDLE SWINGS ON BOTH SIDES ON THE ALT. MDA WAS 1520 FT. AS ACFT LEVELED AT 1600 FT FULLY CONFIGURED WITH AUTOPLT ON; ATC ADVISED US WITH A LOW ALT ALERT. WE ADVISED LEVEL. WITH A LNDG REF OF 134; WE ONLY NEEDED 153 FPM RATE OF DSCNT. SINCE APCH HAD A LONG FINAL FULLY CONFIGURED; THERE WERE PROBABLY NOT ENOUGH PARAMETERS TO TRIGGER A GPWS ALERT. HOWEVER; IN REVIEW OF FLT MANUAL; FINAL APCH SEGMENT SHOULD HAVE A 1000 FPM DSCNT RATE. LANGUAGE DOES NOT STATE 'SHALL.' ALSO STABILIZED APCH CRITERIA STATES NOT EXCEEDING 1000 FPM RATE OF DSCNT 'BEFORE' DSNDING BELOW MDA. THEREFORE; THIS BECOMES A TECHNICAL 'NO MAN'S LAND.' TECHNICALLY; THIS WAS A LEGAL; STANDARD APCH; BUT IT WOULD HAVE BEEN SAFER WITH A SHALLOWER DSCNT PROFILE IN MY OPINION. THAT ALSO WOULD NOT HAVE CAUSED ATC TO BECOME CONCERNED ABOUT OUR CLOSURE RATE TO TERRA FIRMA.