Eave and overhang in BEopt

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I have a slab-on-grade BEopt model showing a heating use of 76.6-76.8 MMBtu/yr with overhangs of 3' or 4' and an offset of about 3'. This is true for any eave size other than "none." When the "none" choice is selected, the energy use decreases to 69.4 MMBtu. This is for a 4:12 gable roof using R-49 fiberglass so with such a big overhang, roof taper factor should not be an issue. One question is whether I should be making a selection other than "none" for eaves when the overhang choices already describe the roof accurately. I would appreciate some enlightenment about these results. Thanks.