If you are really tall or really not tall, you realize most things aren't sized perfect for you. The same will be with any massage chair. Luckily our massage chair has seen blissful experiences for people 6'6 360lbs down to 4'11 and 90lbs.
Are we going to say the 6'6" per got exactly the perfect spot of his neck as intense as the person 6'2"? No. But that person felt the quality of all the other areas he received therapy was so effective he didn't mention any shortcomings of his neck massage.
The young lady who at 4' 11" might be just under the ideal size for the best neck massage experience, but she didn't say anything negative because the hips, the back, the feet and arms work she received was so effective it was all she could talk about.
Because you are dying to know, id say the max ideal height to get the 100% full max potential would be between 5' 1" and 6' 4". But make no mistake, if you are above or below that, I'd still bet our chair at 90% of max potential would still be the best massage chair for you.