There are a few things missing from the formula:

(1) Variable "A" should be the value of the person's work from the employer's perspective, which should be significantly greater than their compensation (unless you're talking about a self-employed person). Otherwise why did the employer hire them in the first place? For example, in the law practice world, associates are expected to account for revenue of roughly 3x their compensation in order to cover overhead and profits to the partners, so an associate making $100/hour would be making, on average, $300/hour for the firm, so a day of lost work is $1,000 from the associate's perspective but $3,000 from the firm's perspective. I'm sure the discrepancy is even greater for, e.g., people in corporate sales jobs.

(2) Taxes. The fare difference is a business expense so the business should be able to write off some percentage of it.

(3) Retention. If a person is flying frequently and has to sit in the back all the time, they are likely to get sick of it much more quickly than if they were sitting up front (especially if competitors let their employees fly in business).