Seems different winch makes have different figures for optimum entry angle.
Andersen 3-8°
http://andersenwinches.com/aw/downlo...er3.4-3.4F.pdf
Lewmar 5-10°
http://www.lewmar.com/products.asp?id=8150&lid=25358
Harken 5-8°
http://www.harken.com/article.aspx?id=15885
Pontos 5-10°
http://pontos.fr//img/cms/Support/Ma...n%20Manual.pdf
Design of the drum will affect the numbers I guess
So using the numbers for your model & make maybe?
You Ask for acceptable range = how much you can go outside the recommended range.
Any flatter seems is asking for override.
Steeper will for sure be a problem when the line start to ride on the drum base.
I try to follow the install guides..