This would set obj2 from obj1:
Obj2: set y to lerp(1250,410, unlerp(310,-1800,obj1.y))
And this would set obj1 from obj2:
Obj1: set y to lerp(310,-1800, unlerp(1250,410,obj2.y))
You’d only use one of those at a time. Say when you’re moving one you’d update the other.