Adverb

[Brahman]

Could someone tell me whether the underlined adverb has been correctly placed in the following sentences?

1. I strongly propose that he should read at least five or six books by Agatha Christie in a month.

2. I strongly propose that he should read, every month, at least five or six books by Agatha Christie.

3. I strongly propose that, every month, he should read at least five or six books by Agatha Christie.

4. I strongly propose that he should, every month, read at least five or six books by Agatha Christie.

[Tukanja]

1. is OK for me.