Greg,
I try to place myself in the buyers shoes. Since values are tied to financing, interest rates, etc., buyers can only afford a what they can afford. So if I know what the price range is for a given subject property, I use that along with the other features such as square feet, lot size, location, bedroom count (two vs. three). etc. I don't take it to the extreme that narrows my search so much as only a few sales show up or the other way around. I try for a good medium.
IMSHO, comparable does not mean "model match" or "mirror" property, or the opposite, a 1,200 sqft home to a 2,000 sqft home.
May be I appraise in a easier market, but I think your making things harder than need be.
If you have a home that is located in a project with many different price points (1,200 sqft to 3,000sqft) or one that is located in a water front community where as some are water front and some are not, I would search by a price range along with my other important features. Many appraisers are taking it to the extreme in both ways. Some are including too many sales that are not comparable and the others are making the search way to narrow.
Fannie wants to know the market trends specifically for the subject property and comparable sales like the subject property, not for every property type that is located in the neighborhood. Which I agree with. A 1,200 sqft home with a price point 0F 120K may have a differant market trends/conditions as compared to the 2,000 sqft home with a price point of 180k that is located in the same subdivision/neighborhood.
For rural properties, even Fannie says in their guidelines that in some situations that an appraiser may use "sales" that are not really "comparable" because that may be all that is available. So just because you use "sales" in the grid that are not really "substitute" properties, it does not mean that you have to include it in the data for the 1004MC.