Try setting the sweep time in the API to 1ms instead of 6 seconds. With 1ms the sweep time parameter will be effectively ignored and it will use the minimum sweep time needed to achieve the 1Hz RBW which will be 2-4 seconds depending on window function. If you set the sweep time to 1ms, this will mirror the settings used in Spike more accurately which it sounds like is working for you. Spike also uses the API, so if you are able to find settings that work in Spike you simply need to mirror them in the API to get similar results.
Regards
