Suppose you have a regular steel drum with an ablative heat shield on the bottom. Theoretically, could this steel drum with heat shield perform a reentry from low earth orbit?
The steel drum may be enclosed in a spherical heatshield covering all sides of the drum. If the ablative heatshield is thick enough, the drum will survive the reentry without damage by heat.
If you want to use a heatshield covering the bottom of the drum only, a stable orientation during reentry is necessary to survive reentry. So the drum would enter with heatshield first.
To protect not only the bottom of the drum but also the top, a conical heatshield is needed. The diameter and height of the cone should be big enough to shield also the top of the drum. The flow of very hot gas over the surface of the heatshield should not touch the top of the drum.