I can recall some previous HIT ideas to keep pushing it after reaching MMF. Can’t remember who supported it (though it wasn’t Dr Darden).
There is no benefit passing the boundary of your max positive rep effort.
That being said, there is a difference doing a negative rep when you’ve reached MMF, as in the original 30-10-30, due to the fact we are 40% stronger in the negative phase.
Even Dr Darden has backed away from MMF, recommending stopping 1-2 reps short of MMF (though “compensating” with shorter rest in between excercises).
To sum it up, there is a difference between training your muscles and the nervous system. Stay away from grinding after you have reached MMF. Not entirely sure why it affects your sleep, but I remember a couple of too demanding workouts, when I couldn’t get my heartbeat down afterwards - which affected my sleep negatively.