Movies diff size

i have noticed that some movies are compressed to a full 4.38 gig
some others are only around 3.8-4.1
the movie i speak of is evil dead thx -dts version
clone tells me with menu & no extras that it will be 91%
after it is done the file is 3.87 gb not 4.38gb why is this??? :confused:

Clonedvd compression is an approximate estimation. Your actual compression may be different.

but should clone not try to maximize the compression and ALWAYS go to 4.38 gb :confused:
why make the film 3.8 gb when you could have 4.38 and use less compression??