The message of the saying is that you only think that grass is greener because you're not living with it. The grass isn't actually greener on the other side of the fence
okay so that would apply if you could see the dirt, but if we're just talking about a thick turf layer it seems like the top would be greener because that's where most of the reflection is going
well, you're saying the grass looks less green because of the dirt, but then you're not talking about how green the grass is you're talking about seeing dirt