How do large national firms like Baker Tilly or Andersen price extremely complex individual tax returns compared to smaller firms?

Large national firms serving ultra-high-net-worth clients charge fees that are 'competitive to the work' involved on complex returns, and clients pay well into seven figures overall for that level of service. One participant recalled that at a large firm, a 1040 engagement was never less than $10,000, even for simple 'children's' returns, and cited an example of a single client's 1040 requiring a whole team of people and costing about a quarter of a million dollars, with a return that ran roughly 10,000 pages. These clients expect a corresponding level of service and will contact the firm at all hours. The complexity and length of these returns is exactly why heavy investment in technology is needed to service them.