I agree with the previous posters that the center rear position is best, and that LATCH isn't necessarily better than the seat belt. LATCH is just suppose to be easier and that is not even always the case. Also, that the best way to check the CSS is with the child to arrive harnessed in a CSS that has already been installed. Otherwise, they really can't check everything.
ALWAYS read you manual completely prior to installing a CSS (Child Safety Seat). I hope that your CSS is not a 5pt harness that adjusts in the rear, as those are a serious pain to adjust vs the front adjust 5pt harness. Here are a few tips on properly harnessing the child in the CSS.
Dress the child normally, no thick clothing or jacket. Bundle around child after they are harnessed in the CSS if more clothing is required for warmth.
Child should sit fully back against seat back and bottom, no space behind or underneath the child.
Harness should lie flatly against the child without any kinks or twists.
Harness height, where webbing threads through the back of the CSS, for RF (Rear Facing) should be at or below the height of the child's shoulders.
Harness should be so snug on the child that only a finger can be inserted, between the harness and the child, on each side at the collarbone level and no slack or room remains, if so then tighten harness and recheck.
Harness retainer clip should be at the child's armpit level, and threaded or buckled correctly as per CSS manual.
CSS handle should be positioned in an approved position when transporting.
Base should be snugly belted in vehicle. Grasp the base at the belt path and attempt to move it in a straight line sideways at the belt path. The base should not move more than an inch side to side or front to back at the belt path. I strive to have no or virtually no movement when I'm installing them. The recommendation is to check the base/CSS before use.
Most infant carrier CSS snap, click, or make some sort of noise when connecting to the base. You should ALWAYS pull the 2 apart or lift up on the CSS to ensure that they have securely locked together, even if you did hear them lock together. If the base is firmly fastened in the car and the child is firmly fastened in the harness, but they are not securely connected together, then someone could still have a bad day.
Check that the recline angle is at 45'. The CSS should never be reclined more than 45', but as the child gains head control the angle can be more upright, as little as 30'.
All of these things should be mentioned to you when go and get your CSS checked. These are things that you need to know NOW and that I thought would help you with you anxiety prior to getting the CSS checked by a CPST. Below I am sharing things will apply now and later.
The following are considered 'Best Practices' and are the safest recommendations that parents can follow.
Keep children in the back seat until age 13.
Read car seat and vehicle manuals and follow them.
Have a CPST (Child Passenger Safety Technician) inspect your vehicle,
CSS, and child.
Rear face as long as possible up to the limits of the seat.
Keep your child harnessed as long as possible (65 or 80#).
Use safest position which is center rear if possible, AND IT IS MOST
OF THE TIME.
Keep child in a BPB after they have outgrown high/weight limit of
harness, until they fit the vehicle seat. 5 things are required for a
child to fit the vehicle seat BEFORE they no longer need a BPB.
1. child can sit all the way back in the seat
2. child's knees comfortably bend at the seat's edge
3. lap belt falls across upper thigh/lower hip NOT tummy
4. shoulder belt falls across the middle of the chest and shoulder
5. child has the self-control to remain still and stay put
HTH