The demand for unprecedented performance in the
upcoming 6G wireless networks is fomenting the research on
THz communications empowered by Reconfigurable Inteligent
Surfaces (RISs). A wide range of use cases have been proposed,
most of them, assuming high-level RIS models that overlook some
of the hardware impairments that this technology faces. The
expectation is that the emergent reconfigurable THz technologies
will eventually overcome its current limitations. This disassociation from the hardware may mask nonphysical assumptions,
perceived as hardware limitations. In this paper, a top-down
approach bounded by physical constraints is presented, distilling
from system-level specifications, hardware requirements, and
upper bounds for the RIS-aided system performance. We consider
D-band indoor and outdoor scenarios where a more realistic
assessment of the state-of-the-art solution can be made. The
goal is to highlight the intricacies of the design procedure based
on sound assumptions for the RIS performance. For a given
signal range and angular coverage, we quantify the required RIS
size, number of switching elements, and maximum achievable
bandwidth and capacity.