Cable Tray Sizing for parallel 4/0 VFD cable

[MyNameJif]

Hey all, long time lurker, first time poster.
I am designing a cable tray system to carry the vfd cables required to run 8 250HP motors, running at an FLA of 276A. With the temperature derating at 82% with a record temp of 105F, I am running two 4/0 VFD TC-ER cables in parallel (Belden 29532C). With the diameter of the cables being 1.536" and using eaton's B-line excel sheet cable tray calculator, we came out to a sum of diameter of 24.58", directing us to use a 30" cable tray. Going with the 6" rails and 9 inch spacing. Distance is about 300ft per run.
The conundrum that I'm facing now is rereading 392.80(A)(1)(c), where it reads that "Where multiconductor cables are installed in a single layer in uncovered trays, with a maintained spacing of not less than one cable diameter between cables, the ampacity shall not exceed the ambient temperature-correct ampacities of multiconductor cables, with not more than three insulated conductors rated 0 through 2000 volts in free air, in accordance with 310.14(C)"
Is this saying I cannot have the cables next to each other as the calculators might suggest, or is it saying I now need to derate additionally due to air flow restrictions? I feel like I either need to recalculate for air flow restrictions, or space them by a diameter and either gets 48" tray, or stack two 24" trays.
Thanks,
Jif

 

[JoeStillman]

392.80(a)(1)(c) Is not requiring additional derating. It is just saying you don't get to use the free-air calculation method (represented by table B.2(3)) unless you have one-cable-diameter worth of spacing. Without the extra spacing, you just use table 310.16 (which is not for free-air ampacities) along with its ambient temperature correction factors.