most synthetics can be run happily at 40:1.
25:1 is fine, just a waste of oil to a degree...smokey as well. the newer oils work better at the higher ratios...
in synthetic two stroke oils, they are using a light base or a deep base . light bases are used by the most common oils and 30 - 50: 1 is the leanest I would run these oils. motorex fully synthetic is a deep base oil and I have run this quite successfully with no issues at 100:1 in the new kato, the old husky and all the powered tools in the shed. id still be using but the kato shop closed and I love the smell of the castor 727...