Flood and Drain Pre-Veg

We are having issues with the rock wool slabs VS Large rock wool cubes in our flood and drain resi, the slabs are retaining the water/nutrients for a WEEK vs the cubes which are 2 days.
(Photos attached showing small clone cube resting on growth slab extension)

From this stage we are transplanting into pots for Flower with clay balls and covering/building up to right level. (Photo attached)

has anyone had this issue? trying to work out how often to water once transplanted taking into consideration the water retention.

Also thinking we will go back to the larger cubes for the next crop to go into the Flood and Drain to allow for better nutrient flow.

Photos for Post

Gotta just try to keep the medium squares the same size if possible.

For now, maybe hand-water the bigger slabs a little and extend the flood interval time? Don't wanna rot those roots out, that's for sure.

Yunnan Kali seed?