Think about this: when you set up on a leg press machine at the gym and you're buttressed against your sacrum, against the pad at the bottom of that leg press.
Sit on the legpressmachine and place your feet high on the platform, spaced widely apart so that only your heels are resting on it at the top outside corners.
On the bench machine, I am doing approx 25reps x 250lbs / 230/210 to failure at progressively lower weight, and the legpress, I am doing 50 - 65reps x «almost the stack», or 250 lbs +.