Is the car seat rear facing or forward facing? We have a Britax Advocate that we have rear facing in both our X5 and MDX and initially had the same issue. Britax recommended using Styrofoam pool noodles or a rolled up towel under the edge of the seat to adjust the recline. Worked like a champ!

Edit for reference from Britax user manual:

Here's PDF of car seat manual: http://www.britaxusa.com/uploads/cms...P363400_R1.pdf

Noodle/Towel tip on page 19, step 8, bullet 3 for rear-facing, shoulder/lap-belt installation.