What are the spiciest slow burn romance books?

Of the 20 slow burn romance books smutrecs.com has rated, the spiciest are Blood Mercy (about 5/5), Twisted Lies (about 5/5) and Things We Hide from the Light (4/5). 6 of the 20 are rated spice 4 or 5, on a scale from 0 to 5.

1. 
   Blood Mercy by Vela Roth spice about 5/5
2. 
   Twisted Lies by Ana Huang spice about 5/5
3. 
   Things We Hide from the Light by Lucy Score spice 4/5
4. 
   Shadow in the Ember by Jennifer L. Armentrout spice about 4/5
5. 
   The Dare by Elle Kennedy spice about 4/5
6. 
   When the Moon Hatched by Sarah A. Parker spice about 4/5
7. 
   Starside by Alex Aster spice 3/5
8. The Fiancé Dilemma by Elena Armas spice 3/5
9. 
   This Could Be Us by Kennedy Ryan spice about 3/5
10. 
    All Rhodes Lead Here by Mariana Zapata spice about 2–3/5
11. 
    A Dance with the Fae Prince by Elise Kova spice 2/5
12. 
    Accomplice to the Villain by Hannah Nicole Maehrer spice 2/5
13. 
    Daughter of No Worlds by Carissa Broadbent spice 2/5
14. 
    Hurricane Wars by Thea Guanzon spice 2/5
15. 
    The Book of Azrael by Amber V. Nicole spice 2/5
16. 
    When You Least Expect It by Haley Cass spice 2/5
17. 
    Wings So Wicked by Emily Blackwood spice 2/5
18. 
    Payback's a Witch by Lana Harper spice about 2/5
19. 
    Taste of Gold and Iron by Alexandra Rowland spice about 1–2/5
20. 
    Assistant to the Villain by Hannah Nicole Maehrer spice 0/5

Each book page lists the sources behind its ratings. Ratings marked "about" are estimates. How we rate