The 1% adjustment is outdated sports science and overly simplistic thinking.
Any adjustment to incline is dependent on the velocity you choose; remember that if there is some wind outside, you'll have a tailwind some of the time, or a crosswind and a much greater cooling effect overall. This will lower oxygen cost and RPE. Heat buildup on a treadmill can easily raise oxygen cost, this effect dependent on duration, velocity and incline.
Obviously, you are not running at lactate threshold. The threshold concept is similarly outdated. Just get a good workout in and try not to stress about it or get caught up in
formulas.