With the incidence being primarily set by the lower wing saddle an the cabane struts, some trial fitting of the interplane struts should show what is right. It sure seems to me that the longer ones would go in the back.

As I recall, the H9 Camel has a faily flat bottomed wing. The aft strut would then be the longer one, as the lower wing airfoil changes thickness (gets thinner) in height towards the rear much more than the bottom surface of the low wing changes in height towards the rear.

The front strut is not far from the lower wing high point on the airfoil, so it makes sense to be the shorter one.

I have done a couple of ARF WWI biplanes lately and they were all arranged with longer aft interplane structs, due to the way the airfoils change thickness.

I could certainly be wrong, but a go either way with an incidence meter would tell the tale.