FIX: Sensitivity did not work by default

Forums without previously calculated scores would return the same values
for low/medium/high sensitivity. Now those are scaled based on the
default value.

The default value has also been changed from 10.0 to 12.5 based on
observing data from live discourse forums.

app/models/reviewable.rb

@@ -78,6 +78,12 @@ class Reviewable < ActiveRecord::Base
     )
   end
 
+  # This number comes from looking at forums in the wild and what numbers work.
+  # As the site accumulates real data it'll be based on the site activity instead.
+  def self.typical_sensitivity
+    12.5
+  end
+
   # Generate `pending?`, `rejected?`, etc helper methods
   statuses.each do |name, id|
     define_method("#{name}?") { status == id }
@@ -195,11 +201,13 @@ class Reviewable < ActiveRecord::Base
     return Float::MAX if sensitivity == 0
 
     ratio = sensitivity / Reviewable.sensitivity[:low].to_f
-    high = PluginStore.get('reviewables', "priority_#{Reviewable.priorities[:high]}")
-    return (10.0 * scale) if high.nil?
+    high = (
+      PluginStore.get('reviewables', "priority_#{Reviewable.priorities[:high]}") ||
+      typical_sensitivity
+    ).to_f
 
     # We want this to be hard to reach
-    (high.to_f * ratio) * scale
+    ((high.to_f * ratio) * scale).truncate(2)
   end
 
   def self.sensitivity_score(sensitivity, scale: 1.0)