How can CAs optimise their client fees

Even though you are billing both the clients in similar fashion technically only client A’s work is adding value.
To overcome this drawback try adopting value-based pricing or provide pre-packaged services to clients. Pre-packaged services involve listing all of the services you provide and attaching a price quote to it. However, the best strategy to fix the cost of the package is by trial and error. Check the maximum price your clients are willing to pay and then stick to it. When it comes to value pricing, there are two areas of concern - self-belief and communicating in advance. To determine the price of the service, evaluate the value of the service for the client, that it how it can benefit him. Remember to communicate the price/terms and what you do for the client before you start.

The systems and processes adopted

Large accountancy firms with state of the art systems, can still end up with lousy work. At present times, you have access to multiple free or affordable software online, utilize them. But an essential part lies in encouraging your staff to adopt these new changes by providing them with the adequate training.
Without the necessary training your workforce will fail to utilise the resources at hand. Install additional screens, provide them with proper knowledge management and document management systems.

Buy electronic working papers, procedures, and checklists. Buy high-speed scanners and other suitable software tools. Take a CA loan, improve the systems and processes involved, overhaul your business to reach your goals.