Revenue Threshold for Business Reversion: Is This Typical?

I’ve just joined a new agency, and I’ve noticed that the commission structure for new business includes a minimum sales threshold of X. Specifically, when a new business deal is closed, the initial X amount is allocated back to the business, and the commission percentage is applied only to the remaining revenue (after subtracting X).

For example, if X is set at $1K and the total revenue generated is $20K, the commission percentage would then apply to $19K.

Is this a common practice in the industry?