The key issue in strategic sites is are they essential to the delivery of the strategy - so you cant set a national site size threshold. It depends on the type of area and scale of development. The SEA approach you suggest is flawed. There is a small sites exemption in the SEA directive but only if the strategy applies to a small site or area. There is a solution. Remember it is the strategy that it is being appraised not site by site, so it it the cumulative impact of the sites that need need to be assessed and reasonable alternatives to the strategy. To give an example if you had 200 SHLAA sites but only 20 long list sites over 200 units you could assess the total impact of different combinations of the smaller sites by area and assess alternative site options for each settlement. The West Berks inspector was very critical of the SEA there for not assessing alternative options around Newbury, just the total number of houses, and they had to go back a step. Look at Wiltshire for a good example of how to mix planning/assessment of sites by community area and strategic sites.
