You're welcome and sorry for the delay. Let's break this down a bit. A 4 week duration task with 100 hours of work means 25 hours per week or 63% peak units. If during the first week, the resource only accomplishes 10 hours of work, then the remaining 15 hours of work he or she is scheduled for will be redistributed.

On a Fixed Work task - Project adds two additional days - 8 hours for the first day and 7 hours for the second day. The 5 hours per day originally scheduled for first part of the task is not increased. The Remaining work is 90 hours but the duration has increased to 4.38 weeks and the peak units has increased to 100%.

On a fixed Djuration task, the 15 hours of work is kept in the same duration - but the scheduled hours of work per day is increased to 6 hours per day - 30 hours per week. The peak units is increased for the entire task to 75%.

For a Fixed Units task, results is the same as a Fixed Work task. The duration increases, the 5 hours per day still holds until the last two days where the work is at 8 and 7 hours per day.

So, if you want the work per day to increase, but the duration stay the same - use Fixed Duration tasks and project will re-distribute the remaining work evenly.

I hope this helps.