Definitely no expert here, and would never override anything that the Reese tech people suggest, but:
The Reese Dual Cam setup manual says the "chain should be as straight up and down as possible". http://www.reeseprod.com/content/dow...ion/N26002.pdf
In a case where the chain swings (non dual cam setup), I can see where straight up and down would be very important. But the chain on the dual cam does not move at all.....just the spring bar moves over top of the cam. Did the Reese tech know that you were using the Dual Cam setup vs. just spring bars ??
If moving the propane tanks forward will get the chains straighter, then that is a good solution to the problem. However, before doing that, make sure that the crook of the spring bars are squarely on the the dual cam when the truck and trailer are straight in line (pg 8, figure 14 on the above link).......that might straighten the chain some if the dual cam is too far forward of the spring bar crook....but it would have to be way off to get rid of 1 1/2 inches.
IMHO, the round bar setup is the way to go on the smaller trailers. The round bar setup seems to be the best fit for trailers with the coupler mounted to the top of the tongue frame, vs the bottom where many of the heavier, longer, taller trailers have those mounted.
Make sure the round spring bar setup is parallel with the trailer tongue. frame.