This is influenced by the contacting surfaces of the mandibular and maxillary anterior teeth on mandibular movements. There are limitatons which influence the anlge of the Incisal guidance;
- ridge relation
- arch shape
- ridge fulness
- interridge space
- aesthetics and phonetics
Elaaborated on in Essentials of Prosthodontics by S. WInkler, between chapters 10 and 15
You will also find the information required on the topic Compensating curve.
The information provided here is some of the information needed you will find the rest in Winkler book.
Have fun. Good luck