Next time you'll go in the box ask someone to do the landing and call up the flight control synoptic page and observe surfaces deflection during the decrabing. Moving the wheel to decrab will ask for flight spoilers to go up and increase drag/reduce lift = sink rate increased. I've tried at 400 feet also but then it sinks if you're not proactive on the throttle. AT is programmed to respond fast to wind gust only, PFC and LAM will help you for pitch, not for speed. In both cases a small application of power smoothen the thing.
My best technique so far, scary for people in the back (I imagine because I'm only flying the box) is to kick the rudder at 20 or so. By the time you ve finished compensating in roll with wheel the speedbrake will be already out and at least one of the mains on ground.
One thing to know about the box and wet runway. We can tune the water depth for the airline it is part of subjective evaluation of the box. So it is different from one box to an other if not in the same company. You might find it easier on one box and terribly hard on the other. Regulation states 3mm or less for water (meaning 1,2 or 2.99 are acceptable values).
Happy landings.