I’ve just added a small amplifier to my setup, very inexpensive, and doubled the received messages as well as extended the range.
0.01-4GHZ 21DB Wideband LNA Amplifier Module High Gain Low Noise Amplifier HAM Radio RTL SDR LNA Amplifier Broadband https://www.amazon.co.uk/dp/B076ZDBGJZ/ref=cm_sw_r_cp_tai_5Ra8Cb9AZ5PDJ
Used a SMA coupler to connect it directly to the SDR, and 5v power from the Pi GPIO header.
A very effective addition to my setup. I’ve ordered more for my other stations too.
This is a very wide band amplifier which will not only amplify 1090 MHz, but also TV, FM and Cell/Mobile signals and may cause overload of SDR’s front end.
It is likely that by adding a 1090 Mhz Filter, the reception will improve further.
Would an Uputronics 1090Mhz Filtered Preamp together with the FlightAware 1090mhz filter (Dark blue) increase any range/performance?
The flightaware filter should be unnecessaray when using filtered preamps.
Filtered preamps are a very good investment in my opinion.
After a proper tuning of the gain 
Thanks for all the advice. I’ll look at a filtered amplifier next
Have a look at this one then: https://rtl-sdr.com/new-product-rtl-sdr-blog-1090-mhz-ads-b-lna/
What antenna / cable / receiver are you using for your stations?