punkalouver a search for ‘type 4 fluids’ might help with your question.
Also see
AEA Recommendations for De-Icing / Anti-Icing of Aircraft on the Ground Twentieth Edition September 2005
The specific point about spraying parked aircraft is the problem of using thickened fluids (type 2/4) as an overnight anti frosting agent. These fluids can dry out (glycol content evaporates) leaving a powdery residue of thickening agent, colorant, etc. The thickener can absorb many times its own volume of water and thus freeze in flight.
There have been incidents involving aircraft flying with a dried-out anti frosting layer, which rehydrated in cloud/rain, formed a gel which then flowed/collected in ‘aerodynamically quite areas’ i.e. control gap/hinges, and froze.
Use of a type 1 fluid before flight washes off any dried-out fluid residue, irrespective of de/anti icing being required.