Fredericks' corset are corset in name only, they are not a real corset.
This is not to bag them, they make some nice clothes. But the corset range is designed to look like a corset without the heavy construction required to cinch you in like a real corset. As such I would suspect that the boning is plastic and the stitching etc is designed to fit firmly, not tightly. This is confirmed by this quote from there website
"Our corsets are not designed to train your waist. Initially pulling too tightly can cause damage to the grommets in your corset."
If you want to get the cinched in effect from a real corset you will have to pay a lot more. the price range is $200 and up
Do not over tighten otherwise you will damage the garment. Just lace firmly.
Here are some links to real corset makers;
Email me if you need more info. Good luck