S RANK?

I'm playin it through on easy to get all the secrets to make the rest of the game easy to go through.

first time through at 4:11 with 19 florites and a level 3 gauntlet (can't remember the # of souls absorbed) = A rank

i shave an hour off my time and find the last florite and app. the same number of souls, and i get a B RANK?!?!?

so through again, at 2:15 all florites, but only a level 2 gauntlet, and i got a B rank again!

so i guess absorbing the souls is my issue. Does anyone know the criteria for an S rank?

Also, when do i get access to the north gate (with sand bags in front of it). i'm guessing a higher difficulty level.

thanks for the help in adavance