Recycling Group Finder - Optimised SQL

finder_development=> explain analyse SELECT *, (ACOS(least(1,COS(0.659296894483735)*COS(-2.13662186884198)*COS(RADIANS(groups.lat))*COS(RADIANS(groups.lng))+ COS(0.659296894483735)*SIN(-2.13662186884198)*COS(RADIANS(groups.lat))*SIN(RADIANS(groups.lng))+ SIN(0.659296894483735)*SIN(RADIANS(groups.lat))))*6376.77271) AS distance FROM "groups" WHERE (defunct = false AND lat is not null and lng is not null and full_address is not null and full_address != '' AND groups.lat>36.8764220242163 AND groups.lat<38.6734369757837 AND groups.lng>-123.556101941199 AND groups.lng<-121.282729058801 AND (ACOS(least(1,COS(0.659296894483735)*COS(-2.13662186884198)*COS(RADIANS(groups.lat))*COS(RADIANS(groups.lng))+ COS(0.659296894483735)*SIN(-2.13662186884198)*COS(RADIANS(groups.lat))*SIN(RADIANS(groups.lng))+ SIN(0.659296894483735)*SIN(RADIANS(groups.lat))))*6376.77271) <= 100) ORDER BY (ACOS(least(1,COS(0.659296894483735)*COS(-2.13662186884198)*COS(RADIANS(groups.lat))*COS(RADIANS(groups.lng))+ COS(0.659296894483735)*SIN(-2.13662186884198)*COS(RADIANS(groups.lat))*SIN(RADIANS(groups.lng))+ SIN(0.659296894483735)*SIN(RADIANS(groups.lat))))*6376.77271) ASC, num_members DESC LIMIT 30;
                                                                                                                                                                                                                                                                        QUERY PLAN                                                                                                                                                                                                                                                                         
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 Limit  (cost=29.19..29.20 rows=1 width=364) (actual time=1.153..1.159 rows=30 loops=1)
   ->  Sort  (cost=29.19..29.20 rows=1 width=364) (actual time=1.152..1.155 rows=30 loops=1)
         Sort Key: ((acos(LEAST(1::double precision, (((((-0.423756013910457)::double precision * cos(radians((lat)::double precision))) * cos(radians((lng)::double precision))) + (((-0.667232757379067)::double precision * cos(radians((lat)::double precision))) * sin(radians((lng)::double precision)))) + (0.612561252574016::double precision * sin(radians((lat)::double precision)))))) * 6376.77271::double precision)), num_members
         Sort Method:  top-N heapsort  Memory: 40kB
         ->  Index Scan using index_groups_on_defunct_and_lat_and_lng_and_full_address on groups  (cost=0.00..29.18 rows=1 width=364) (actual time=0.124..0.979 rows=67 loops=1)
               Index Cond: ((defunct = false) AND (lat > 36.8764220242163) AND (lat < 38.6734369757837) AND (lng > (-123.556101941199)) AND (lng < (-121.282729058801)))
               Filter: ((NOT defunct) AND (full_address IS NOT NULL) AND ((full_address)::text <> ''::text) AND ((acos(LEAST(1::double precision, (((((-0.423756013910457)::double precision * cos(radians((lat)::double precision))) * cos(radians((lng)::double precision))) + (((-0.667232757379067)::double precision * cos(radians((lat)::double precision))) * sin(radians((lng)::double precision)))) + (0.612561252574016::double precision * sin(radians((lat)::double precision)))))) * 6376.77271::double precision) <= 100::double precision))
 Total runtime: 1.235 ms
(8 rows)