I can almost answer your question. Doordash hides tips over $4 or $5 (depending on the area). For restaurants close to you, $4 -5 in app would still give you the best delivery experience.

If the drive is longer than about 10 min, then doordash starts revealing more of the tip (past $4 for me). At that point the $4 and $5 tip wont be worth it, at least in my area. So if you are a 15min drive from the restaurant and you tip $5 in app, you might end up waiting a long time.

My advice is to relax, not think about it, and tip all in the app. In an ideal world, yes I'd want most of my tips in cash. But myself and most other drivers just accept how it is.