Below the DH for your approach (which is supposedly the CAT I DH of 200 feet if we're talking manual landings) nobody guarantees you sufficiently accurate ILS guidance. Whenever the aircraft is required to fly the ILS until touchdown, low visibility procedures are in force for this exact reason - to make sure that a holding aircraft or a passing truck will not give you an ILS signal glitch. Hence, blindly following the FDs below DH can be risky. Your scan should alternate between inside and outside, with more focus on outside as you get lower. The touchdown zone should stay in the same point of the windshield. Once you get to the flare, you should be looking about 100 metres or so ahead of the aircraft. If you're looking straight under the nose, you'll likely flare too low or not flare at all which can result in a hard landing. If you're looking too far ahead, e.g. to the opposite end of the runway, you might flare too high - which, if not corrected promptly, can result in an even worse hard landing compared to the low flare scenario.