when i got my bow with the help of the bow pro at the shop we set my sights and so on

when i went to set my pin i wonted it set 10 20 30 but the pro said toset it at 20 30 40 so i did. He said by setting it at 20 i could shoot from 0 to 20 with no proplem because under 20 it is so close the diff wont matter.

is this true. And if not i gusses i need to go slap the guy lol