In my limited experience, I would say that that can definitely be a big part of it. Another consideration is your software: I know in Beersmith, they attenuation figures for yeasts are all in manufacturers' ranges, but you may likely get better than the average of those limits. You can adjust the setting by editing your yeast. I know I regularly get WLP001 to finish above 80% when that is the top of the range from White labs, and that is fresh pitches from a starter, no re-pitching. Everyone else can add more, and will likely say it is your better yeast management practices, and I don't disagree