Not that I’m aware Harley, as long as you meet the generic minimum length I think the house mostly irrelevant.  Most ranches with a short roof (that is low pitch) that I’m familiar with have around 12’ chimneys, mine and a friend at work are that way.  We both were having draft problems, he extended his chimney and told me he couldn’t believe the difference and what prompted me to get an extend-a-flue as part of my major overhaul to improve my draft. 

A flex pipe, ovalized, through damper, and 12’ long will work but you have a risk of problems usually during warmer weather.  My insert with a liner at 12’ long, ovalized, and mis-matched was unuseable unless 45F or less outside just couldn’t draft.  I was irritated to turn on oil heat, and since draft stunk my glass would get dirty until it hit 20F- outside.  But, at least at 20F or less outside I got enough draft for things to run smoothly.  I extended my chimney from 12’ to 16’ in total and improved other draft problems and now even when it’s 58F outside I can have a fire going and on reloads only a hint of smoke will pour into the living space, and pretty much the glass has been spotless since.  But, as far as I can tell between my coworker and I the difference between 12’ and 15’ is really noticeable on draft and if you get 15’ you’ll get a lot more enjoyment out of it (that’s to say, it’s best to work on getting 15’ in our opinions than trying to do things to make it work with 12’).