Oh! I have been hanging the shirts the wrong way up for 50 years now. You live and learn 
I do hang some of my tops, jumpers by the shoulders otherwise they seem to get longer at the sides than in the middle back and front iyswim.
The reason I put underwear inside is because it is thinner and dries more quickly than other things, the lines on a rotary line are smaller, things get progressively larger and thicker as my washing progresses outwards on the line, ending with towels and bedding on the outside.
And I wouldn't want the nice man next door to see my Bridget Jones's knickers.
Logic applied to the washing line 
(larger and thicker - is that me over 50 years as well?
)
Royal Mail threatens to stop deliverys over dog attacks
a note of caution if you use mouth wash

. In case anyone's interested, I have an ancient rusty rotary line - my tatty knickers and socks are always (modesty