Why 3 hops?

Many people and documentation seems to say 3 hops is "fine"...seems like that isn't enough for what I'm seeing the typical usage? After getting a node to be portable nobody ever seems to see the messages at just 3 hops, minimum seems to be 4.

It looks like the "usual" topology in my area anyway is people have "a node they use", then "a node on/outside of their house", and there's then 1 node looks to be on a tower or something in the region. So I count 4 hops minimum:

1. What you use -> one higher on your property with a yagi/rooftop
2. your yagi/rooftop node -> the regional tower node 7-10 miles away
3. the regional tower node -> someone else's yagi/rooftop node 7-10 miles again
4. their yagi/rooftop -> their device they carry to use

And then to get past "the one regional tower" would require minimum of 5 hops?

So why is it everyone says 3 is enough?