20 gig for 1.2 hours is a bit excessive and i'm sure you're exaggerating anyway...
Most normal length, 1080p movies, that are newer, and filmed digitally compress really well and you can get to 8-10gb without any noticeable quality loss... The biggest thing that'll make them bitrate hungry is film grain... All that random shit that changes every frame does not make it easy to compress. Fargo 1080p took me 14gb and The Good, The Bad, and The Ugly 1080p took me 16gb. They are both 3 hour, old, grainy as hell movies. The 4GB flac audio file for Good/Bad/Ugly didn't help (it was a 5GB DTS-MA stream).
"Scene" encoders aim to meet a filesize, which is retarded IMO. I've seen a shitton of scene encodes that are bitrate starved, and some with bitrates over 20mbps...which is higher than the original bitrate on some blurays :/
x264 encoders aim for transparency... They actually run tests at different settings/bitrates and compare frames from source/encode, and try to find a bitrate that isn't ridiculous, but and encode that matches the source extremely well. Most people won't notice the difference (like mp3 compared to flac), but it is what it is. Harddrives are cheap, I'll go for quality
http://jorsher.com/upload/x264/grantorino/ <- gran torino, 8gb
http://jorsher.com/upload/x264/goodbadugly/ <- the good, the bad, and the ugly, 16gb
Fargo is the grainiest piece of shit I've ever came across. The bitrate I settled on was around 15mbps, but I'm going to re-encode with a newer build of x264 and see how it turns out...