Is [a] always [a]?

[ReneZ]

Hi Marco, yes this is all true, but of course there are exceptions to just about everything.

Strings of i are not rarely preceded by o instead of a.

Also, I have seen cases where the r in iir looks more like s, but has still been transcribed as r.

Edit:

By the way, I really like the graph in You are not allowed to view links. Register or Login to view.

It has a lot of interesting information, e.g. it seems to say that k and t tend to have a different context, while that of r is more similar to t.