CASPers are dropped from around one hundred miles above the surface protected by a fairing that separates at some point no higher than ten miles over a planet's surface in order to ensure compliance with the Galactic Union's strictures against firing weapons at planets from higher distances.
From the Books: "He and the rest of his First Platoon were dropped from Phoenix 1 at just under one hundred miles above the surface as the dropship executed a steep, powered climb, effectively firing them at the planet below. Topsol was rated Human Nominal with a thicker-than-normal atmosphere, so his CASPer was fitted with a fairing to shed heat. The ten CASPers burned in, accompanied by twenty decoys – nothing more than thin ceramic alloy weighted shells that provided extra targets for ground defense."
- Cartwright's Cavaliers, p. 148.