I have a question too. I have a Britax Decathlon for my nephew and I'm having the hardest time getting it installed facing backwards in the infant position. Any tips? The tether straps aren't long enough to lock it in. Is the middle the best place to put him (only place with the metal bottom tethers, so that's where I placed it.
What vehicle do you have? I suggest you start by checking the owners manual for it's information on LATCH (Lower Anchors and Tethers for CHildren). Most (though not all) vehicles don't allow you to use LATCH in the center. There are usually a set of LATCH anchors for each outboard seating position, and they can not be used for the center. If the LATCH straps aren't reaching, than you may be trying to use the anchors in the wrong seating location.
The middle seat is the safest as long as you can get a good installation. If you can get a better installation outboard (side), than that is safest. Also, if you want to keep the carseat in the middle, you can install with the seatbelt. LATCH is not safer than the seatbelt, it was simply designed to be easier.