Yes... It is the 89 number you want to change. But.... When you change it, be sure to do an M502 to load the 'default configuration.h setup' and then an M500.
You should be able to measure how much it extrudes when you say extrude 10mm. If it extrudes 15mm, you would want to change the 89 number to 89*10/15 which would be 59.
You should be able to measure how much it extrudes when you say extrude 10mm. If it extrudes 15mm, you would want to change the 89 number to 89*10/15 which would be 59.