If you do 1x1 and long both and ES jumps 30 points and VIX drops 2.00 over the course of a few days because of positive news and lack of concern then you lose net. This happens often where ES jumps and vols come in hard so 1x1 ratio just has no edge.
You can do this with lots of investments: Commodities, Forex, Stocks, Bonds, ETFs, Options, Real Estate, CDs. You can go long or short in two or more different securities or instruments. You can buy two different instruments because you know they are not inversely related but they are going the same direction (Commodities:Long- Coffee & Heating oil late summer/ fall/winter). EurJpy & UsdJpy short because they are going the same direction. Retail stocks: Walmart & target late summer/ fall/winter because they are going the same direction. Stocks in a bear market? sell stocks and buy bonds. The bottom line is that each type of investment will present both long and short opportunities, either in each individual security (by the short or long-term charts) or instrument or in a related security or instrument. You can also research correlation. Like you mention, it is not 100% but when it happens it is nice. I have had many successful trades balance out the funds in my account this way. Sometimes trades will automatically close themselves out when they hit a certain profit threshold based on activity between two instruments.
So now is the time I would be looking to do this spread. I would short 1 vix future and short 1 ES future. Vix really pumped here. Currently Vix future is 19 and the ES is 2089.
If you had the reverse on overnight, you would be up about $500 on each 1 to 1 spread. Vix future up about 3 and ES down about 50. This is a great way to play vol and the 1 to 1 ratio seems to work best for me. You can always tweek it a bit if you are bullish or bearish.