Not exactly sure what you're looking for, However....
If one is looking for the correct spread ratios for the Soy Crush spread, the ZS x 10, ZL x 9 and ZM x 11 mimics the Crush Margin process the best. It is also acceptable for a 1-1-1 Crush Margin (aka poor man Crush spread). One has the Jan., Mar., May, Jul., Aug., & Sep. crush, and Nov. ZS vs. Oct. Products, Nov. ZS vs. Dec. Products Crush.
I currently have all the Soy complex Crush Spreads compiled from 1975 to present.
Now in terms of the "correct" ratio for ZS vs. ZL or ZM products, or ZL vs. ZM in terms of volatility...? That's hard to answer. Volatility varies over time and varies for a given time frame. Example:
HV for ZMF3 on 3/1/12 was: 1 month = 4.22%, 2 month = 7.51 %, 3 month = 9.13%, 6 month = 13.78%, 9 month = 16.48%, and 12 month = 20.18%.
The attached shows the average (all 6) volatility for the ZS and ZM on the Jan. 2013 contracts. Based on the small sample I put together for this reply, an increase in the volatility of 1 is reflected in the other.
What I do to plot spreads in the ZS vs. 1 Product, or ZL vs. ZM is convert the price to equity value, then one less the other.(or Long less short) I also have all these compiled back to 1975.
To look at all the spreads with a ratio of contracts based on Volatility one must ask..."The volatility over what time....? A default historical volatility of all contracts over a long period....? And once such a ration is computed, what's the objective.....long one short another to profit with reduced risk...? Profit from a change in the HV...?