No he won't. He can't. If your gross increases and you are paying the same amount for liability insurance it means: you were paying too much originally, or your gross is low enough that you stay in the bottom tier of rates even with the increase.
What would you think if you went down to the welding supply and bought a pallet of welding rod every month, then your workload increased and you started buying 3 pallets of rod per month and the welding supply charged you the same amount for 3 that they used to charge for one?
I'd love to go down to the Dodge dealer and get 2 one ton trucks, and pay the same price I did for one. It doesn't happen.
Bechtel is not paying the same amount as you for liability insurance. People who gross 5 times what you do, aren't paying the same as you either.
You're paying the insurer to protect you from liability from a failure of a weld, more welds made = more liability = higher premiums.
JTMcC.