I think you're confusing this with the 60 GHz band (WiGig)
Pretty much everything from VHF and up (all of wifi) is line of sight only. Not just the mm-wave stuff. Cell phone networks only work because the telcos pay big money to get their transceivers power/data up on towers high above the terrain.
Store and forward meshes assume the nodes will eventually see each other but down at 5ft above the ground they often won't.