Author share is relatively easy to calculate. If I send 0.100 steem to your bot and it upvotes for an equivalent of 150% of that, then I'm getting an upvote worth 0.150 steem. 75% is the author share, which is ~0.112 steem.

My suggested text does not account for curation rewards and it explicits it is based on author share alone. We all know there wll be some curation rewards and that we don't know for sure how much it will be, so it's fine.