If soybean oil is used in such low concentrations as .5%, why wouldn't using higher concentrations be better? Is there something preventing a higher concentration being useful or effective?
Some oils are helpful at controlling some insect problems. They suffocate the insects and are not toxic to humans or animals when properly applied. The problem with using higher concentrations is that a concentrated solution will burn or kill the plant. Solutions that are not toxic can also be problematic as they will dry to a sticky surface that will pick up dust and soot and reduce photosynthesis.
As well in the summer oils must not applied when it gets too hot (over 90 Def F or ~32 deg C).
Even with the problems of applying at the right rate at the right time horticultural oils are an effective control of soft and slow insects like scale. Real success means you must observe the plants and weather and know what pests are expected.