Why are some .MKV files larger than others?

[tkmops]

Does anyone know why some one hour(42mins) TV programs(720p HD .MKV)encode out to 1.1GB to 1.4GB, while others encode out to as much as 2.18GB? At first I thought it might be the source material, that bluray, or HDDVD, or HDTV was more 'dense' than the others. But, that doesn't seem to be the case, as I'v seen up to 2.18GB for all 3 sources. It is that one encoder is more knowledgable, and thus able to encode a one hour program into a smaller file, than another encoder?

Is there a way to shrink these 2.18GB files down to the more 'normal' size of 1.1GB, and still retain the
720p HD? Oh, and yes, I have checked these files for 'extra' languages with 'mkvmerge GUI'-they have nothing to strip out, just the one video file, and the one audio file.

Thanks!:)

[neuron2]

Is there a way to shrink these 2.18GB files down to the more 'normal' size of 1.1GB, and still retain the
720p HD? Oh, and yes, I have checked these files for 'extra' languages with 'mkvmerge GUI'-they have nothing to strip out, just the one video file, and the one audio file. The nature of the files itself is suspicious, but then you say you had to look into the files to see what they contained, where if you had encoded them yourself you would know that. Closed for rule 6 violation.