Rack Mounting.
Your great-looking rack is clamped to the head rest tubes and it looks sturdy.
If you overload your bag either with a one-time load of lead bricks
or stress it over years of use with water bottles, any welded load-bearing
tubes may fail at the welds.
This is part of what I used to do:
Test-ride racks and rack-mounted accessories to destruction on the road,
riding road bikes/motorcycles.
If you damp the road vibration between your head rest tubes and
your rack, then your rack will last you much, much longer.
Effective damping with inner tube shims between the clamp(s) and
the head rest tubes, rubber washers, rubber grommets and the like
will work wonders.
Or not, depending on how much you've over-designed your rack!
Sincerely,
Steve