V.W.
First, let me say that I am no expert and that these are questions that you definitely should talk to your doctor (or doctors) about.
However, from what I have read, it is my understanding as well, that the small particles are the "bad" ones. That the big fluffy particles are not. While I am NOT advocating making any changes without discussing it with your doctor at length, I will share that I did a low-carb diet several years ago (to lose weight after pregnancy), totally on my own. Not consulting a doctor, lol. (Do as I say, not as I do). The very lengthy book that I read (somewhat like a textbook) discussed how lowering your insulin response (low-carb reduces the amount of insulin your body produces, and insulin does a lot more in your body than JUST deal with the sugar in your bloodstream--insulin is a hormone and affects/helps regulate all sorts of cell function), results in more of the big fluffy cholesterol particles and fewer of the small more sticky and more damaging ones. I did not have my cholesterol tested, as I have never had issues one way or the other and was in great health to begin with, just doing the "diet" to drop post-pregnancy weight.
But if you are interested in reading what the book had to say on the subject, it was called, "The Protein Power Life Plan" by Drs. Eades.