A distinction is made between 'here' and 'there' with respect to the location of the speaker, but so 'this' is a demonstrative and ka is an adverbial. One can say ye so 'this thing' but not *ye ka 'that thing.' For the latter one might have to say ye so ka 'that thing over there.' Despite this observation, one does get noun phrases like the one assumed above. See Examples 122 and 123. Samarin (1967a) has very little to say about ka.
In Example 122, although ka seems to be a constituent of a noun phrase, I'm not inclined to accept it as a demonstrative. One does not contrast melenge so 'this child' and *melenge ka 'that child.' For the latter I think that one would say melenge so ka. Compare with what one can say in Ngbandi: lo ka a-ga [3SG there PM-come] 'He's coming over there' (Lekens 1958: 310B).
Source: Samarin 1967a: 80
Source: Samarin 1967a: 241