This, according to FMSCan, is what you are likely to be receiving: https://fmscan.org/main.php?l=-1.958333 ... th=cannock
Looking at your spectrum, a quick look suggests it is clean without any overload, or signals where there shouldn't be. If that is the case, then that's a tribute to how relatively bombproof the S3 is. I'm trying to crunch the numbers to see how strong SC is above the noise, but you've done the scale in S units rather than dBm or dBuV lol. I think if my calcs are correct, R3 is 80-odd dB above the noise.
If FM breakthrough into other bands when the FM antenna is connected is the only problem you have, then you're doing pretty well. A physical antenna switch to switch it out when not needed is probably your best solution.