<Sigh>
I can see that they are different sizes. Let me see if I can get the picture posted for discussion purposes.

OK. The one on the left is longer, ergo the rear post. But if you notice, the bottom of that post, before the first shoulder of the flange, is only 5mm long. The front post's is 8mm. These portions of the posts insert into the recesses on the luggage rack bracket. On my brackets these recesses are both 8mm deep. The rear post is 3mm short, so it does not seat properly; the flange rests on the bracket instead of the post resting inside the recess.
So, do I have the wrong Easy Bracket posts, the wrong luggage rack bracket, or the wrong place & time.