Got about 4000 hrs on CRJ & we used to find lots of very thick clear ice on the UNDERwing after having landed in cold temps (melt & Run back ice), even when the overwing was clear. I used to go around scraping it off with a plastic ruler. De-icing trucks can find it very difficult to de-ice under the wing. Warm fuel can help but can cause melt & re-freeze (harder to see)if the ice is not removed physically after it starts to melt.
I once picked up a brand new one at montreal & on the acceptance flight test the Bombardier test pilot said they could already measure the diference in wing efficiency from the first flight of the aircraft due to flies & stuff on the leading edge. That is how unforgiving this wing is. I would never be tempted to go one second over minimum holdover on this A/C.