The vehicle manual requires that you recline the seatback all the way to install a ff'ing seat.
Make sure that the Blvd is set so that the mechanical recline is in upright mode, then place the seat on the vehicle seat so that it's mostly straight up and down. You'll find the back of the base is off the vehicle seat a little, but when you get in to the carseat, the weight will compress the vehicle seat enough that the back of the base will be touching the vehicle seat.
Here's a pic in my 07 Outlook of a MA - same shell as the blvd.
Base on seat:
How shell sits between the sculpting:
Top of shell from other side - you can see how it pushes against the headrest here:
Full side view:
(bottom 2 picture was taken at a separate time from the others so the base may be in a slightly different position on the seat. This particular install was fairly upright.)
This is what the back looks like for the tether: