I need to patch these holes in the subfloor where the vents are. These holes are from a return vent that is being moved, the joist cavity below these holes is a return duct. I'm assuming using blocking would affect the airflow. Is it acceptable to patch the subfloor right in the middle of a joist where you would have 3/4" of the patch on the joist and 3/4" of the existing subfloor on the other half of the joist. Or should I use a larger patch and go past the joist and use blocking. Do the other two sides of the patch need to be supported. The subfloor is 3/4" plywood and the joists are 16" OC. The slate floor and laminate floor in the picture have been removed and the finished floor will be either hardwood or an engineered floor. How do I patch this and not affect the airflow in the return vent.