h, s, s-hacek in Iranian

[Vidhyanath Rao]

The recent discussion about retroflexion in IA raises, for me at least,
a question about Avestan and Iranian in general.

In Iranian, PIIr *s becomes h, PIE *k' becomes s and the
ruki-conditioned s becomes s with hacek. Can these three be stuffed into
just two phonemes? In particular, can h and s-hacek be considered
allophones of a single phoneme in Iranian?

Regards
-Nath