Shouldn't the rear tire have considerably more tire pressure than the front if it carries 60% of the load?

If the rear carries 60% if the load and the front only carries 40% proportionally the rear should have 60%/40%= 1.5 more times air pressure (assuming tires are equal width).

I used to run my rear Tufo at 180 psi and my front at 130-140 for best results. (actually 180 rear/120 front would be correct if weight distribution was 60/40).