You can increase this further by abstracting away the "code monkey" aspect.

1. Specialize & productize your output, then offer fixed pricing. Customer gets a predictable result for a predictable cost, you produce something you can estimate to good accuracy while earning a higher effective rate.

2. Retarget your deliverables on business value instead of a technical spec sheet, then charge accordingly.

Note that both of these involve business development strategies, not improved technical skills.