The rear door may not be the designated accessible entrance and it may not be a designated accessible means of egress, but it is there, customers do use it, so it is "a" means of egress. As a component in a means of egress, it is regulated by chapter 10, not chapter 11.
And here’s the first thing in Chapter 10:
Buildings or portions thereof shall be provided with a
means of egress system as required by this chapter. The provisions of this chapter shall control the design, construction and arrangement of
means of egress components required to provide an approved means of egress from structures and portions thereof.”
The structure is the sentence recognizes there are components NOT “required to provide” an approved means of egress.
You took a leap based on, hey, if someone can get in through the back door, they must be able to get out the back door, so it is a means of egress.
That’s the first assumption, and it may or may not be true. The OP didn’t provide that information.
Next, you quoted chapter 10 but didn’t use the “required to provide” scoping of 1001.1. The OP did not say that their exiting analysis concluded the back door was a required means of egress. It might; or it might not.
Here’s the rest of 1012 in the Florida Building Code:
1012.2 Slope
Ramps used as part of a
means of egress shall have a running slope not steeper than one unit vertical in 12 units horizontal (8-percent slope).
The slope of other pedestrian ramps shall not be steeper than one unit vertical in eight units horizontal (12.5-percent slope).
Your previous posts seem to be mixing ADA and FBC chapter 10. You / we simply don’t have enough info from the OP to render a code compliance opinion that is based on Chapter 10. There may be a scenario where a 1:8 slope with 4’ landings complies with Chapter 10.