You should call the companies that modify vans for handicap use. I am sure they would have the info you need. They may also have info that you have not thought about.

 

Thanks. I'm not ready to spring for the expenses to modify a van. I was hoping someone here might be able to measure the opening heights for me.

 

@johnhon
Here is what was mentioned in the past:

Problem with opening height of tailgate on 2019 Honda...

The non-power tailgate on my 2019 Honda Odyssey EX only opens to, a head bashing, about 5 ft., 10 in. above ground level. The tailgates on my 3 previous EX's all opened to much more than 6 Ft. The dealer tries to tell me this is normal. I can't believe Honda would made such a horrendous...

www.odyclub.com

Also read some of the messages before and after above reference point.

 

Detailed Interior Dimensions for 2021/2022

If this doesn't help, then you should probably go to a dealership and measure it yourself.