blocking off the first 6 rows and last 4 is a weight and balance rule called rule 2 which if under 132 pax is used if the zfw balance units exceed the limits or if more than 178 pax once again only if the balance limits exceed then you can subtract 0.4 balance units from the aft and add to the forward balance units ie with a limit of zfw 42000-43999 the balance limits are 5.4 to 5.8 it would then become 5.0 to 6.2 if your zfw was say for example 42455.9 hope that makes sense.