Our family is considering a puppy from a litter that have a Sire that is on the larger size. He weighs over 22lbs. I believe the mom is around 18 lbs. They come from a very reputable breeder but because we travel a lot by plane and wish to take our Cavalier in the cabin with us we were hoping for a one that is under 20 lbs. What would be the likelihood of getting one that is under 18 lbs. from this litter? My common sense says the bigger the parents the bigger the puppy but wasn't sure if this was the case. Thanks for your help!