I have to admit that there was some inconsistent goofiness on this matter in the first edition of Dialogue Editing for Motion Pictures, which I am (trying) to sort out in the new edition.
Without going through the reasons (I was probably over-influenced by an unending series of hideously noisy films when I wrote 1ed) I was, indeed, over-dependent, or at least vague, on radios. With luck, the message in 2ed will be:
Ask the mixer what s/he wants. Don’t be a nudnik, but get a general sense of mix strategy, preferences, and division of labor.
Favor the boom, whenever possible, for all the obvious reasons but don’t write off the radios. Be aware of noise issues with the boom.
It’s possible to cross cut between boom and radio, but it can be tricky.
There is a place for boom in radio-driven scenes. The opposite is also true. Avoid unnecessary tone build up.
“It depends.”
Ask the mixer.
Thanks for pointing this out.
John