Difficulty installing FPSVD? Not secure enough?

[FunkyB&PunkyC]

My friend just purchased the FPSVD, and is trying to install it in a Chevy Blazer (not sure what year). She is having difficulties getting it in very tight and snug. Has anyone else had this issue, are there some tricks to getting it in just right?
Also does anyone know if the manual is available online?
Thanks in advance.

[lovinwaves]

What year is the vehicle? What is she using to lock the seatbelt? The seatbelt must be locked somehow to get the carseat to move less than an inch. Is she installing it FF'ing or Rear-facing? Is she using LATCH or Seatbelt?