buddy,
i'd say more than one hedgie involved(diff funds+ diff risk levels = diff size of position) . It would be a very big punt for one fund to accumilate over 5% on a possibility that they will raise the bid . Risk probably outweighs the net gain.
Also if someone was accumilating to beat zfx to the punch they would be better imo to accumilate over %5 and say "Hey look at us we've go %5 what have you got"