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Hunt sell a regular or slim version, maybe that would do it?
https://www.huntbikewheels.com/products/shimano-sm-hb20-hmb618-centre-lock-ring-for-disc-rotors-to-fit-around-15-20mm-front-bolt-through-axles -
I dont think your fork can flex 1mm so close to the axle.
The lockring from this shimano kit is only 2mm thick (but is more annoying to tighten as the tool can slip easily( and has 1mm more threading than other lockrings so could bottom out))
https://www.bike24.com/p280551.html
Like so...