Hi there, could you expand? You mean in my case approx. 85kg of my 90+ would go through the hand?? And via the arm into the shoulder? I do practice "soft ukemi" from some throws, but have always seen the hand as a means of orienting my body to distribute impact evenly, rather than taking impact itself.
I would disagree with Greg's recommendation too. In my practice, the slap is an add-on, with the main part of the energy of the fall absorbed through the structure of the body as smoothly and softly as possible.
Training on a wooden floor in the past has taught me that slapping in ukemi is not something you should be in the habit of relying on...