Modify instance parameter before the instance on points node, based on the position

Question

I'm trying to make a grass field, and make flowers bloom when a 'sun' approaches the ground. I have already solved the problem of making the grass taller and increasing the flower size, but I would like to add the blooming animation of the flower. Right now I have a node group that given an input between 0 and 1 creates a flower, closed with 0 and fully open with 1. The problem is that when I try to instanciate flowers on top of the grass I just get the same flower repeated over and over, based on the distance between the 'sun' and the original position of the flower. Basically I would need to know the distance between the flower and the sun before instancing the flower. Does someone have a nice workaround for this issue?