Move the ME workouts to days where you can do them in hills then. Just allow good recovery after.
If you can get that burn, even on the box then the pack is too light or the step too small. MORE WEIGHT!! Seriously. I’ve had guides with very strong legs needing to use full 40% of BW to get the ME effect.
Its actually easier to get it on the box than on a hill because most people can’t access steep enough hills.