Let's look at the same kinds of factors but using three cameras with different characteristics but the same lens.
Sony 𝜶6xxx, 𝜶7R4, 𝜶a9.

The biggest print without upsizing can be made with the 𝜶7R4 (42.9"), closely followed by the 𝜶6xxx (40.9") and way behind will be the 𝜶9 (26.9"). These numbers will change with lens, subject size and distance but will remain in the same ratios.

These cameras all have different design goals, prices and so on. If you compare the 𝜶9 and the 𝜶6xxx with equal total pixels, though, then the standard 1.5X calculation is correct. 26.9 x 1.5 = 40.35. But the EFL calculation between the 𝜶6xxx and the 𝜶7R4 simply does not work.

If you don't care, save the electrons. Nothing to see here.