If you mix up a gallon of methanol with 20% castor (or Klotz ) you could then mix it half and half with the hobby store 10%and get two gallons of 5% fuel.
Easy peezy.
Or 2 gallons of the methanol fuel and get 3 gallons of 3.33% nitro.
Ifind it hard to believe it will not run well with a colder plug and 10% nitro.