The aircraft remains in TA/RA mode though TCAS reverts to TA mode at a defined altitude "900 ft AGL stated below" the TCAS will not issue an RA to descend "thought it was 1500 agl" for obvious reasons. Also keep in mind generally aircraft are flying at slower speeds thus the resolution allows for greater distance though time is also calculate, as determined by the pilot(s) TA will allow for the pilot to make a decision and communicate intentions.