SI es correcto mónica.
When Guests give 4 star they consider they are giving you a great ratings, but the APP is not considering this a great review. 5 stars depends on weather, the relation between guests, and so many subjectives items.
What I found hardly achievable is when you run a lot of reservations to have a 80% of 5 star reviews. This is a higher standards than hotels.
This is my proposal:
1. Get SUPERHOST by property not by user. So, if you have some more than one, you are not affected by the worst.
2. Set the bar in 70%, not 80%
3. EXCITE THE GUESTS to understand if the recommend the place then they should rate 5 stars. Otherwise, they may be thinking they are helping with 4 stars review, and they are NOT.