I don't doubt your knowledge Robert but are you sure the main source of income for a Prop firm is commissions?. Because the main source of a Prop firm is the percentage of profit they take from a trader (you make money we make money). Commission is secondary (since its very low compare to a traditional broker). What you said is for a brokerage firm (their only source of income is commission).I work for Lightspeed, a division of Lime Brokerage. The software is owned and sold by Sterling Trading Tech. I'm familiar with the way US regulated JBO prop (Your money as first loss) and traditional prop firms work. JBO firms want little or no risk overnight as the revenues from the firm come mostly from marking up commissions. There is no business model where it makes sense to allow the risk of leverage overnight accept an active long/short equity or option portfolio.
