Possibly paddlers height vs weight ratio doesn’t actually make much difference ? For everyone all weight is not applied directly onto seat under spine as we all have legs and arm forwards.
But there’s not that much weight on feet, majority is onto seat. So centre of gravity for any person is certainly not out near knees, probably more likely directly under sternum, or a little bit in front of that. If that’s right, and I’ve not tested this in anyway, the CoG of tall vs short paddlers would only change by a few centimetres at most & compared to having 3 metres plus of hull front & behind would probably make bugger all difference to balance when floating. Although saying that perhaps my own drink bladder tests having 3 litres (3kg) under knees or behind seat disproves my wavering thoughts.