I did this simple test with a file I just happened to have handy. Not really representative of a typical live recording since it is a studio track, but nevertheless.
"Come Together" by The Beatles.
WAV is 43.7 MB
I take the WAV into Audition and drop the signal by 10 dB and save a new WAV, which is also 43.7 MB
01. Come Together - The Beatles -10 dB.WAV 43.7 MB
01. Come Together - The Beatles.WAV 43.7 MB
Then I FLAC them at various levels ( I did all Level 0 to 8, but these are representative enough)
FLAC0\01. Come Together - The Beatles -10 dB.flac' (ratio = 0.520). 22.7 MB
FLAC0\01. Come Together - The Beatles.flac' (ratio = 0.623). 27.2 MB
FLAC3\01. Come Together - The Beatles -10 dB.flac' (ratio = 0.484). 21.1 MB
FLAC3\01. Come Together - The Beatles.flac' (ratio = 0.586). 25.6 MB
FLAC8\01. Come Together - The Beatles -10 dB.flac' (ratio = 0.471). 20.6 MB
FLAC8\01. Come Together - The Beatles.flac' (ratio = 0.573). 25.0 MB
The content of the file had a bigger effect on the file size than the level of FLAC encoding. A 10 dB difference in overall RMS level made about a 20% difference in FLAC file size.
The ~10% difference (80MB) in size between daspyknows and furburgers Fogerty FLAC file sets could be accounted for probably ~5 dB difference in RMS level. If someone wanted to compare the WAVs they would probably find something like that. I don't care enough to do so. I would venture to guess daspy's recording has more dynamic peaks and furburger's (from a cassette) has more compressed peaks.