The durability issues with Fox coils is due to flex causing misalignment between the two shock ends. Leverage ratios don't play into it. You can run a DHX2 on a bike with more extreme (DH bike) or less extreme leverage ratios with no issues. Because the upper end of the shock is rigidly mounted, any flex out of plane will cause significant bending loads. Also if the yoke isn't perfectly in line with the shock it puts the shock in bending. A shorter yoke isn't less prone to being out of line with the shock, but it won't apply as large of a bending moment. This loading actually affects all shocks to some extent. Air shocks are more rigid so they aren't prone to snapping, but they do go through bushings faster than on other frames.There is a recent thread somewhere on this forum where a guy with a new Levo SL broke a DHX2 shock shaft. Damaged his frame. Fox sent him a new shock but Spesh won't do anything for his frame as the shock is not approved for use on the frame.
The Fox is not approved for 'yoke' style suspension linkages. Apparently it's not flex or alignment but has to do with leverage ratios but I don't know that for certain.
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Now a bit on what makes some coils fine to run and some not. Stiffness of a solid circular cross section is proportional to its radius to the fourth power so a larger diameter shock shaft makes a huge difference. If you compare a 9 mm shaft to a 12 mm shaft (assuming same material) the 12 mm shaft is 316% stiffer. Having a hollow shaft does decrease stiffness a little, but it's often still stiffer than a smaller solid shaft. The modulus of elasticity plays into it as well, so a steel shaft will fair better than an aluminum shaft. Fox's shock shafts are steel, but they are the smallest out there so they don't handle the bending well. That said, because they are steel they will generally bend before catastrophic failure. I have no issues with running a DHX2 on frames with a long yoke, but I do periodically inspect it for signs of bending. This can include blowing out the piston seal by the way. So if your DHX2 is leaking there's a chance it's also bent. I would run the DHX2 over a Super Deluxe coil for this reason actually. Because the Super Deluxe has an aluminum shaft, it will show no signs before breaking and will fail catastrophically.