Resource calendars

Your test combines two separate controls: the resource’s working calendar and a plan configured to keep task duration fixed. Fixed duration does not preserve eight hours of effort when other scheduling inputs change, so a two-day result is not guaranteed. Display effort, duration, and assignment allocation together before and after changing availability. Then test a newly created plan using Fixed effort, after IT permits project-level overrides, and compare identical assignments. Microsoft documents that scheduling mode is selected during project creation, not changed after saving. The bookable-resource calendar describes that resource’s availability; it is not a separate allocation calendar for each project. Keep its capacity at one and represent project allocation through assignments rather than fractional calendar capacity. Resource calendars therefore are not inherently pointless in Fixed duration. I cannot confirm the forthcoming Capacity View’s exact behavior from these settings alone.