Land does play a role in an appraisal of similar homes, incrementally. Your home on half an acre is still one home on one lot. For a home to be on only 1/16th of an acre it must be a row house or town house? 1/16th of an acre is only about 2700 sq feet +/- / Are these smaller homes as well as being on smaller lots? You say you have comps at $250 to $270 per foot. - Are they really comparable? If the townhomes at $250 per foot sold were only 1200 sq foot ( $300,000 ) and you are mad because your 2000 square foot home is only $211 a foot ($ 422,000 ) Then you are trying to have an apple compared to orange (instead of apple to apple) Price per square foot is routinely higher for smaller homes than it is for bigger homes.
You probably have no recourse against the appraiser. The appraisal is just one professionals opinion. The appraiser would certainly have annotated his appraisal document with the limitations of the scope of the appraisal. Several of those limitations are worded to protect them against people who disagree with their opinion from taking action against them.
Immediately after the low appraisal you and the buyer had options to save the deal. Best for you would have been if buyer had been willing to come up with cash for the difference. Best for the buyer would have been if you had lowered the price to the appraised amount. Sometimes a compromise can be reached at a mid-point.
If that buyer is gone forever, you must now start fresh. Ignore the appraisal and ignore your old asking price. Ask a realtor to give you a fresh market analysis. Offer (insistently) to pay a BPO fee (Broker Pirce Opinion Fee) of $75 to $150 since you do not intend to use a Realtor for the marketing (you said you are selling on your own).
Only a accept a free market analysis is there is a possibility that you might use a realtor in the future.
Do not be too discouraged. Sales do occasionally fall out of escrow. Even if you had a Realtor, it still could have happened. Some really great Realtor might have saved that deal, but we can never really know.