Hi,
in structures like modal + auxiliar + past participle, I think the usual position of adverbs is after "would", "should", "could", "might", etc. That's where I've always put them. I agree.
But I think that sometimes you can put it before the past participle. Yes. Where should I put adverbs in strucures like the following?
I would have asked her to join the club. - (probably, definitely, never, only, even, also, etc.) Both positions are possible. Usually, and in general terms, the position that is nearer the front of the sentence serves to add more emphasis to the adverb. Of your examples, words like never/only/even are more tied to the verb, but other adverbs like probably/definitely can be positioned pretty freely, eg even at the front of the whole sentence, if you wish. All of the following are possible, although some are more common than others.
Probably, I would have asked her to join the club.
I probably would have asked her to join the club.
I would probably have asked her to join the club.
I would have probably asked her to join the club.
I would have asked her, probably, to join the club.
I would have asked her to join the club, probably.
What do natives do? I also think they don't contract "have" as "I would probably've asked", <<< actually, I'd say we do this quite a lot but they might say "I would've probably asked". Yes
Best wishes, Clive