The cold temperature effect at DA is less than at the FAP - the higher you are above the elevation of the altimeter setting source (in the case of LNAV/BAro VNAV this is the aerodrome) then the greater the cold temperature effect. So, at -30C, the height difference at 300ft above aerodrome is 60ft, while at 1500ft above aerodrome it is 280ft. Furthermore, the Obstacle Assessment Surface is set back an additional 0.3NM from the point at which the 'MOC surface' meets the ground so you have at least 322 ft of vertical clearance, after taking account of depressed VPAs, at any point along the final approach.