When mapping dense vegetation, why is it better to fly higher?

I have a P4 Multispectral drone and I plan to fly over dense woodland and use the point cloud produced in Pix4D Mapper to map the canopies of individual tree crowns. I am reading about how to plan the ideal flight for this purpose and a recurring piece of advice is to fly as high as possible and have as high overlap as possible. I can understand the purpose of having very high overlap but I do not understand why I should fly as high as possible. If anything, it seems counterintuitive- surely the point cloud will be more accurate if the drone is closer to the vegetation and can ‘see’ the trees more closely? Can anyone explain to me why it’s better to fly higher when mapping dense vegetation?