How Oracle Supply Plan interprets forecast versus sales orders when both are entered in same month

I have a question regarding how Oracle Fusion Supply Planning interprets manual demand (or forecast) versus sales orders when both are entered for the same time bucket.

For example, let’s say that for the month of September, I enter a manual forecast of 1000 units. In addition to that, I also input three sales orders on different dates within September, with a combined quantity of 800 units. However, when I run the supply plan, the system still shows the total demand as 1000 units, not 1800. It seems as though the system is not adding the forecast and sales orders together, but rather treating the forecast as a placeholder to be consumed or replaced by actual orders.