Thanks, Julie.
But this seems to work only when I manually change the duration of specific task.
I would like project to automatically do that during Leveling of the whole project, so for the times that a resource is busy (with Task1) in 40% the parallel task (Task2) will automatically get 60% Level, and when parallel task (Task2) continues into time that resource is busy (with Task3) by 20%, the task (Task2) will become 80% Level.
I realize that for perfect optimization of resources I expect that Leveling (or other) function will be able to automatically split the work, and also to modify the Level of each part of that split work.
Is this possible somehow?