I used to use linseed oil with the 1-shot and had good results controlling flow but I've had hit & miss luck trying to add forms of solvents with odd paint brands. Some have curdled. Some refused to dry. Some developed adhesion problems. I would have done the entire signs with all 1-shot if I hadn't had the bulk of my supply stolen from the farm.
When it comes time for lettering/graphics on the funnycar I'll avoid these cheaper paints.