Kapusta, I am no habitual practitioner of vasikin. But just from what I remember learning in Brachos, there is first, an inyan of semichas geula ltfila, which means we must have no break between gaal yisroel and shemoneh esrei. In addition therte is an inyan to daven smack at sunrise either because of zerizin makdimin (zealous people try to do things as early as possible) or also because of a pasuk Yiraucha im shemesh (let them see you HKBH with the sun). Because netz is the earliest possible time lchatchilah, we time shmoneh esrei to begin right after netz. But since gaal yisroel is the final bracha of shema, and must lead into shemoneh esrei, we must conclude shma right before netz so there is one continuos flow from shema to gaal yisroel to shemoneh esrei.
Note shema and talis and tefilin can be before netz, as long as they are after mishaykir (light enough to recognize a friend at distance of 4 amos). This is about 50 minutes before netz.
This is my understanding, but I am not an expert.