Unable to Set Spark Promotion Listing to Topics Only

I tried changing the reply limit on my Spark Promotion listing to 200 so that it would display topics only, as the listing shows that 200 posts have already been made. However, the system doesn't seem to allow me to set the limit below 250.

Could you please look into this? I'd like to set my Spark Promotion listing to display topics only without having to increase the limit to 250.