I'm not an authority on this, but I think you would want to keep the ratio even lower than 20%...maybe more like 5%
With biodiesel you can run it straight into your engine from the tank as normal, but I think with SVO you need to have a separate tank with heaters. Need to ensure the SVO gets to about 130 degrees or so as it is being injected to prevent coking. And then a purge from the injection pump to ensure that it doesnt gum up the IP.
Has the price gone up since I last looked at it? It was 1.45 a gallon when I saw it a couple of months ago.