HRe: SE8300 - Under floor heating, slow down the internal control aplication or write a lua script?
Only the proportional band is configurable on the SE8300 (from 3F to 10F). I would recommend a LUA script that takes into account the slab temperature and reacts accordingly.
Patrick Dumas from the Montreal Viconics office might have a script already done or can provide some insight. You can reference me as Patrick and I both joined Schneider when Viconics was acquired in 2011.