Please Help!! Inconsistency & Confusion..

Ok everyone, thanks for reading. I hope someone can help me out. I have been having some real inconsistency trying to rip/burn my dvds. Here's what I mean:

I know the final disc image needs to be 4.36 GB or less to fit on a DVD right? (Oh btw, I use MacTheRipper to rip the dvds and then DVD2OneX to compress them if needed.) The problem is: sometimes 4.36 GB fits on my DVD-R just fine, and other times it doesn't! What's weirder is that if I try to compress to a little less than 4.36 GB (like 4.33, 4.29, 4.24) than I do get a little more run-time, just not enough.

What I don't get is why 4.36 GB does work now and again. For example, "Ghost in the Shell" was exactly 4.36 and I got the whole movie to fit perfectly. But when I ripped "Reservoir Dogs" it came out to about 4.33 and chopped off the last 5-10 mins! Does that make any sense at all? No! To top it off I got the "Italian Job" to squeeze into about 4.29 GB... guess what, it lost the last 14 mins.

Is this a problem with DVD2One compression? Or is it bad media? (memorex 8x 4.7 GB) Thanks for any help you can offer!!