It can vary with every horse cause people train them different but for MOST horses its outside leg only to drive them into the lope. I know some horses are different but usually you will only use your outside leg during the lope. Using your outside leg to keep them loping, drive them forward, etc.. I have not heard of putting your inside leg by their shoulder but I am not sure how your horses are trained lol A gelding I ride is spur stop so when he speeds up in the lope you lightly squeeze both legs to slow him down to the proper lope.I usually ride with the rhythm of 1-2-3 outside leg, 1-2-3 outside leg if that make sense. But it depends on the horse
Not sure if this helped? But good luck!