Hover = 50% throttle?

I have a herelink controller where both sticks spring back to centers,
I have an option to make throttle center zero but when I do mode changes from Guided/take off to alt hold and stabilize my copter falls. I wish not to mod my controller.

There has got to be a way to make hover = 50% throttle/ mid throttle does anyone know how to accomplish this in the params?

Alt hold and loiter should automatically put hover at 50% throttle (± some deadband).