When you get upwards facing things failing it can be because the slicer has too few top layers which makes angled faces have gaps. While you may think it is a wall the slicer sees it as top layer. Try increasing the number of top layers and check in the preview how it appears.
Infill will normally support those faces so no separate support is needed. Just make sure you have enough top layers that no gaps form, 3-5 layers should be alright.