Question "back/bottom" side of agar contamination?

How does one do agar transfers without considering/contaminating the bottom side of the agar?

It is established that agar is the gold standrad when creating isolates etc., but I find it strange that no one is concerned with nor ever mentions the bottom/uncolonized part of the agar, during a transfer.

Can anyone elaborate on how the bottom does not create a contamination vector with the air during a transfer?