Max out summary filter at 100 posts.

app/models/post.rb

@@ -240,7 +240,7 @@ class Post < ActiveRecord::Base
   end
 
   def self.summary
-    where(["(post_number = 1) or (percent_rank <= ?)", SiteSetting.summary_percent_filter.to_f / 100.0])
+    where(["(post_number = 1) or (percent_rank <= ?)", SiteSetting.summary_percent_filter.to_f / 100.0]).limit(100)
   end
 
   def update_flagged_posts_count

lib/topic_view.rb

@@ -404,7 +404,7 @@ class TopicView
     closest_posts = filter_post_ids_by("@(post_number - #{post_number})")
     return nil if closest_posts.empty?
 
-    filtered_post_ids.index(closest_posts.first)
+    filtered_post_ids.index(closest_posts.first) || filtered_post_ids[0]
   end
 
 end