Quote Originally Posted by zorro View Post
I'm a little confused now. Would с сестрой be pronounced /z/ сестрой and в войне as /f/ войне so the preposition doesn't blend with the noun?

Z
No, it would be pronounced like

/s:estroi/
/v":"oine/

I think you know what this ":" symbol means in IPA? It means a long sound. In this case a long consonant

So
сестрой - /sestroi/
с сестрой - /s":"estroi/

войне - /voine/
в войне - /v":"oine/