Shirley,
What part of the country are you in?
A red flag to me as a reviewer are adjustments that dont appear to be market supported. For example, In most cookie cutter subdivisions I work in, a lot adjustment is absolutely not market supportable. Many times in these s/d's lots although different in size have the same functional utility and similar privacy, slope, ect.. Buyers in these s/d's dont determine lot size as a predominate factor and all else is secondary. I am not saying that a lot size or location within the s/d is never considered. I am saying that this would be almost impossible to extract from the market considering Scope, Purpose and intended user of the report.
Now having said all that , I will tell you that I work many s/d(high end) that you will be wrong and wrong in a very big way if you dont make an adjustment for lot size. Eastover, Myers Park and Dilworth S/d in Charlotte are great examples. Eastover 1 acre lots are worth approximately 1 - 1.5 million. Myers Park 1/4 acre lots sell for around 600K, 1/2 acre around 750-800k. Dilworth is a historical district and its very difficult to determine some values in here due to the strict requirements of this district, but there are large differences because of a segmented submarket in this s/d.
Making arbitrary adjustments like you have suggested will cause an unfavorable comment in any review I would do on your work. I would even go so far as to question your geographical competency, a clear USPAP requirement. You definitely would be a very unhappy camper after I got done with your report. Any rebuttal on your part would subsequently be trashed as I would then put forth evidence in the review beyond normal summary work to end the discussion.
Take you job seriously and people will take you seriously. Stop trying to second guess readers of your report. It suggest that you dont believe in your on work product.