Sri BhattabhAskara has used the drAviDa-pATha which has 8 prashna-s. The smArtha-s everywhere use the Dravidian pAtha these days - there could be exceptions, and that has 10 prashnas. The 10th prashna that you refer to or the mahAnArAyaNa upaniShad is the 6th in the archive scan and is found in part 2. The 5th is all the 3 valli-s - prashna-s 7, 8, and 9 in the Andhra pATha, or the taittirIya upaniShad. All 3 are combined into one prashna in the drAviDa pATha. He does not seem to have commented on the pravargya or its brAhmaNa - prashna-s, namely 4 and 5 in the Andhra pATha.
Ramakrishnan