I understand "computationalism" as referring to the philosophical Computational Theory of the Mind (wiki, Stanford Encyclopedia of Phil.). From the wiki:

Computational theories of mind are often said to require mental representation because 'input' into a computation comes in the form of symbols or representations of other objects. A computer cannot compute an actual object, but must interpret and represent the object in some form and then compute the representation. The computational theory of mind is related to the representational theory of mind in that they both require that mental states are representations. However the two theories differ in that the representational theory claims that all mental states are representations while the computational theory leaves open that certain mental states, such as pain or depression, may not be representational and therefore may not be suitable for a computational treatment.

From the SEP:

representations have both semantic and syntactic properties, and processes of reasoning are performed in ways responsive only to the syntax of the symbols—a type of process that meets a technical definition of ‘computation’

Because computation is about syntax not semantics, the physical context - embodiment and extension - is irrelevant to computation qua computation. That is what I mean when I say that embodiment and extension are regarded as of no interest. Of course, if a philosopher is less thorough-going about computationalism, leaving pains and depression out of it for example, then embodiment may be of interest for those mental events.

However, your last paragraph throws a monkey wrench into my reasoning, because you raise the possibility of a "computer" drawn to include more territory. All I can say is, that would be unusual, and it seems more straightforward to delineate the syntactic rules of the visual system's edge-detection and blob-detection processes, for example, than of the whole organism+world system.