Height adjusting for ultrasonic sensors - Altitude sensor.

So as part of my project I’m creating a handle that will be attached to a blind stick using ultrasonic sensors to detect whether an object is in range to cause an obstruction to the user.

The 1st sensor deals with frontal obstructions
The 2nd sensor deals with head height obstruction and is angled at a 45 degree angle covering the likes of low hanging branches etc…

The 3rd sensor deals with gradient scaling by checking if the ground scales away from the sensor at an alarming pace such as a kerb or downward staircase.

Now this all great but if I setup the sensors to pick up say 100cm based on say my own height which is 6ft 3" the sensors will work as intended.

However if I were to then pass the handle onto a user that has a height of 5ft 7" then 3rd and 2nd sensors may never go off or might go off when they have no need to due to the height difference.

How can I sort this out? Now I’ve heard about altimeters but I’m only increased in the height difference and whether it is also possible to automatically adjust the sensors accordingly every-time the handle switches between height differences, so that all sensors work as they should.

if any confusion let me know and I’ll try and explain a little more in depth.