As you know there are a number of versions of dump1090 that currently exist and we have started with a couple of them to provide support for the RSP. These are just our first cut at ADS-B and a range of improvements are in the pipeline. The RSP can support a number of modes and we are evaluating the best combination of setup for ADS-B reception. I'm not sure what OS and hardware you are using but I'm assuming you are using a Raspberry Pi 2 or 3 as the mode implemented in dump1090 on our github site will produce overflow errors on the Raspberry Pi 2 and 3.
Also, both of these versions have a hard coded value for gain reduction. This may not be optimal for every situation, the antenna, location, environment will make each reception case slightly different. On the windows version we have done some more work and implemented the command line options so that people can change the gain values and some of the other options to try to tune to their specific situation.
We are also continuing to work on other versions of dump1090 and are optimising the API so that this system will run well on a Raspberry Pi 2/3.
Temporarily you could change the 9 in the following line...https://github.com/SDRplay/dump1090_sdr ... 090.c#L585
which will change the gain reduction value (remember this is how many dB below maximum gain you are), we would not recommend a lower value than 4 or higher value than 28, unless you are using an external LNA, in which case a value of higher than 28 may be appropriate.
When we have an optimal system we will retro fit it to these versions of dump1090 as well as any new versions we implement. In tests here I have not seen the results you are getting so I'm sure your result can be improved. You should also see an improvement using the Windows version which you can download from here: http://www.sdrplay.com/windows.html
We are committed to producing a good ADS-B solution for our customers.