Hi ivoradev ,
Thanks for your post.
I understand you're talking about the products in restock status view in Stock Central, am I right? You can read here how we calculate such status.
If you want to use your formula, you'd need custom development.
It's not possible to send emails when a product reaches the restock status, and we don't plan to add such functionality for now, sorry. However, you can create a thread in the "Suggest a feature" section of this Forum, and if enough people are interested in it, we'll consider adding it in the future.