Leveling issues, "pinning activities in place"

Hello,

For a while, I have been facing some issues with leveling resources on P6. I understand the principle upon which it calculates start dates, but I'm facing issues "pinning" some activities down and forcing start and finish dates.

For example I know that an activity will start on day S1 and finish on day F1, I add the necessary start on constraints to try and pin it in that place, yet it changes dates.

Same issue with in progress activities, where I know approximately when the activity will end, but the leveling sometimes prefers to finish it way later than given in the exptected to finish / remaining duration fields.

Do you know any solution, or a trick to work around this limitation?

Thanks in advance