I let the razor decide.
I ride the cap with my mildest razor, a King C. Gillette, during my final touch-up pass. Allows delivery of a BBS shave with this razor. No need with my moderately aggressive Weishi Long Handle.I have a Muhle R89 & a Phoenix Artisan plastic open comb slant. I've always been using a steep angle riding the guard. I discovered while using the PA plastic that the plastic cap is super slippery when wet. So, I started riding it and the results were amazing. So then I started riding it with the Muhle and for me I find the cap having so much more surface, with light pressure, it feels more stable and is easier to control. Gives me really close first passes. When I occasionally do a third pass, I bring it in and ride the guard. All feels like the sweet spot for me. I guess there's also a more neutral position where you're just blade riding. What do you other gents do?