Back clam add ons

How do “add ons” to back claims typically work?

I saw a chart that states back pains can go from 10-50% based Essentially off of mobility, but then that secondary claims can be added to them to increase the percentage.

I was rated at 10% for breaking 3 vertebrae & “post traumatic arthritis”. I went for a c&p exam today & submitted my claim as a secondary to my 10%, radiculopathy (sciatica).

I was told my claim was changed from a new claim to an increase claim (to my initial 10%). With that being said, how do they rate sciatic pains within that 10-50% scale?

For example, if my back increase goes to 30, could they then give me 10% for each side of my sciatic, totaling my back claim to 50%?

In the scale I read that 50% is reserved for total immobility of the spine, which I don’t have so I’m only anticipating 20-30%, but naturally I was looking at calculators to see what would get my total percentage to 100%, and that numbers 70%. Which seems extreme to get off of this back increase without being totally immobilized.