1/4" is all you want on the rails, with less you have more bottom that gets almost no heat. However, that just shows that Leader is not very close when a pan tag gives the size.
That caused problems for me when I bought my new pans from Thor (in Quebec). I believed the tags on the old Leader pans and ordered a flue pan and syrup pan for the same total but when I got my new pans they were too long for the Leader Arch. The old pans had a 1" thick ceramic insulation between them and I had about 3/4" to spare at the back. The new pans only had a 1/4" gasket between them and they were 1.5" too long. I had to remove the base stack collar and make a new one that was 1.5" shorter from front to back on the arch. My old pans were gone so I couldn't measure them, but I measured the Thor pans, they were exactly as stated (and as ordered). The Leader pans had to be about 2.25" shorter in total length between the 2.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.