I may be completely wrong but that doesn't look how mine looked when it was apart.
I believe the castor angle is 4 degrees. (Forgive with the next bit) Tangent of 4 degrees is 1.15 approx so for every 100mm of vertical separation the top should be 1.15mm behind the bottom. So if the separation is 400mm the top should be 4.6mm further back than the front.
Not sure what the actual gap is but your top looks approx 25mm further back than the bottom.
Plumb line on a bit of cotton dropped from the top would establish.
'course I could be totally bonkers!
