Well, Jambo, over a day and 144 views with no reply. I was avoiding replying because I don't qualify on your
I am only really interested in IRS/GPS updated FMC a/c operators i.e. capable of RNP <1.
criteria. However, I think you've raised an interesting question and maybe my reply will provoke more response than your Q.
The CF is not part of an instrument procedure, of course. I saw something in an AIC I think, to that effect. But I often wonder, myself, why one shouldn't join the O/B leg of a procedure (providing, as you say, one is above MSA) without starting at the IAF. Once established on the procedure one can then descend according to it. Like you, I can't see why not.
OzExpat may have a view on this.
"Self positioning" to achieve the <30deg is, in my outfit's policy, perfectly OK provided ATC are happy with it. As an ex-examiner, I would say this demonstrated good awareness of both the situation and the rules.
Now, let's see if that draws a response...