I experienced something similar with the liftgate on my Odyssey hitting my head. If you've got the power liftgate trim, there's actually a way to set the opening height manually. All you have to do is open it, adjust it to the height you prefer, and then hold the close button until you hear it beep twice. That'll save you from bumping your head every single time
Now, the LX doesn't come with a power liftgate, so there's no built-in way to adjust the height. However, some people choose to replace the struts with longer ones to get a bit more clearance. Just make sure you pick ones that are designed for your specific model to avoid messing up the mechanism
It's a pretty straightforward fix once you know the trick