I know this is an old thread, but I wanted to chime in with a potential workaround for the OP. Instead of cross-posting to your mastodon account, you could enable ActivityPub on your Micro account, then follow it from Masto.
Once you’ve followed it, enable notifications for new posts. Then when you publish new posts on Micro, you will get a notification on Masto (so you don’t have to go hunting for the new post on Masto).
All you need do then, is boost the Micro post with your Masto account. Then, if anyone replies to your post, they will be replying to your Micro post and you should (I think) get webmentions back to your Micro account.
That’s what I’m doing, at least. 