I Have the answer to this problem!
the reason that you can't get a 100% kill is because....
hey scott, is there a spot on your team for another mission builder?
the waypoints are set way too close!
if you set up a mission, think about being in the cockpit!
this way, you'll remember that to keep bombers in tight formation you "must" fly clean!
another words...don't toss the plane around in the sky...bombers turn slow!
if you try to turn too fast, or correct too much on your inbound approch...you will not keep the bombers in close formation!
also, i have recieved a 100% kill on that sub pen...this is how ya' do it...
get close enough to the target ...that you can "target" the sub pen.
then peel away...far enough so when you return to destroy it...you have your whole bomber flight in tight!
this way...when you drop..most..if not all of the bombs will land on target!
another thing that works well is in mission builder...change "spread factor"
from 1.00 down to say..0.80..now you'll have a tight formation to start with.
good luck..and drop those bombs on target!