In ground sprinkler basics - should heads be near the street aimed into lawn?

I have a 50 head system installed by a 'pro'. I paid him so I guess that makes him a pro. but beyond that, I have little faith in him / had an argument with him and not going to have him back (a key think I was worried about was that I have an aerator for my lawn tractor. as long as I avoid the heads, are the pipes deep enough? He told me yes... then I found a 3' length that was barely buried / visible on the surface. so if he can't get my main concern dealt with, what else did he screw up? ANyway.... Are the heads supposed to be near the street shooting into the lawn? Or more in the middle of the lawn shooting towards the street? They are about 1 - 2' from the street aiming towards the middle of the lawn. So there's 1 - 2' behind the heads that don't get water. he said its unavoidable - closer to the street (we don't have a curb / belgium blocks - the grass just ends and pavement starts) and he said they would be more likely to get driven over / chewed up by snow plows. your thoughts?