I used to have to rotate the rear light mounted on the seat post around when I fold my A-bike every time because it affects the folding mechanism.
However, I won an Akslen SL-10R red LEDs safty light from a lucky draw in a party recently.
http://www.akslen.com.tw/SL_10R.html
Then, I replaced that old, cheap and bulky rear light with this cool and tiny “Water Spider” safty light.
Now, the rear light doesn't affect the folding of the A-bike anymore.