Have you tried delivering a leaflet through your own letterbox?
Some are set up by complete dipsticks. Heavy duty spring on the outside one, then a brush system that needs a jack hammer to penetrate it, then a magnetically held inner one.
Then have the whole thing at ground level.
I'm surprised the Post Office doesn't refuse deliveries to houses that can't be civil enough to make it an easy operation.
Nice houses have a light that comes on to illuminate the approach and porch but doesn't blind you. Then the flap opens inwards with a light spring and if there has to be an inner one it too is lightly sprung. If it opens outwards then there needs to be something to open it with, not a section of only one inch projecting a bare 1/16th.
And no silly brush systems. They are completely porous to draughts if they get through a properly fitting main flap.