Now this is not a pure realism suggestion, it is more of: "How to to try to emulate realism with simple game mechanical settings"
First of all, if any dev sees this and says: "It's Impossible to code this" I will lock the topic asap.
Here's the suggestion with some numbers:
Weight: Max FOV
0 120
.1-.5 110
.6-1 100
1.1-1.5 90
1.6-2 80
2.6-3 70
3.1-3.5 60
3.6+ 50