I have always heard that the rack strut should be against the eyelet with the fender strut mounted outside the rack strut. If there is a lot of weight on the rack, it does not stress the bolt as much. Here is
another thread discussing this. I also use Loctite or nylock nuts when installing racks and such to help reduce things rattling loose.
Here's a quote from that thread
Stainless steel M5 allen bolts are the usual solution.
The correct order, from the frame eyelet, outwards is:
Rack
Fender
Washer
Bolt.
If the rack is outside the fender, it has more leverage on the bolt and can over-stress and break the bolt.
Use a washer
Smear the threads of the bolt thinly with some grease (white lithium grease), or at least put a drop of oil on the threads.
On the drive side the bolt can protrude inwards and interfere with the chain. Add more washer or file off the end of the bolt. You need about 1-2 threads protruding to ensure full engagement of the bolt.