Should be no difference.
The floors are all the same wether coupe or convertible.
Probably some marketing strategy on the part of the site you were on.
Maybe in the convertible pack they include mats for rear seat.
Sometimes on coupe mats, if not specified, you may only get front mats.
I have orignal I use for car and had a set made at clothing shop that had set up for
going through floor matts, heavy needled machince needed, so a little reserch required.
Then I oredered plain set from ford, designed my pwn set for my car and had them made
Used twice for car shows