Last Post: October 6, 2006:
From the bold text above, and the text below, I think we can deduce that the RTS/CTS threshold test is applied to the first MPDU produced by fragmentation.
9.2.6 Individually addressed MPDU transfer procedure
"A STA shall use an RTS/CTS exchange for individually addressed frames only when the length of the MPDU is greater than the length threshold indicated by the dot11RTSThreshold attribute."
I hope this helps. Thanks. /criss