Agree, Most higher altitude jets start around 3000 ft. I running super lean changing to larger jets or enlarging the current main fuel jets is the only to enrich the fuel mixture.
If air bleed only jets then going smaller is the way to go.
Even though there is a couple 100 variations of this engine. It looks like the 1.24mm jet was commonly used. So find a bit and check the size to see if some put of the smaller jets in place. I have had resize jets in the past due to usual lean burn problems requiring some choke before the mod.
You might be able to use the 92063-7143 1.26mm or 92063-7144 1.28mm jet from the FX730V since it uses the same 92063-7142 jet in some applications.
EDIT: Had the decimal in the wrong place as jets are list in hundredths of millimeter not thousandths.