[Advaita-l] agnimukha prayOga - a query

[Bhaskar YR]

praNAms
Hare Krishna

Pardon me, my doubt is not relating to advaita vedAnta, it is about 
agnimukha prayOga according to Apasthambha...

Kindly let me know when we can follow 'chatushpAtra prayOga' and when we 
have to follow 'shatpAtra prayOga'...Is there any reference to these two 
type of prayOga-s and viniyOga maNtra-s while doing the agnimukha?? 
normally we say only kriya vAkya without chanting any mantra while doing 
agnimukha, like agneH uttarataH dvAdasha darbhAn saggusteerya, teshu 
pAtrANi dvandvannyanchi, dve-darbhAgre pracchidya, pracchALya, Ajye 
pratyasya, prachee tiratpUrya, sruksruvAvagnau pratitapya, prOkshya, 
nidhAya etc. etc. these are all mere kriyA vAchaka vAkya-s, whether there 
is any veda maNtra to be chanted while doing these kriya-s?? I wanted to 
know in detail. 

Sri Ram prabhuji, Sri Ananda Hubli prabhuji ,  Sri Ramakrishna 
Balasubramanian prabhuji or Sri Karthik prabhuji any help on this??

Hari Hari Hari Bol!!!
bhaskar