yes i understand what you are saying but i believe you have some wrong information.
first, i have a Dart, which is smaller than the Hammerhead, and it has a 2" intake.
for mine, i had to have my 2 1.5" bulkheads feed into 2" piping and Tee off into 2" Tee.
see post 94, page 2 on the above link...