A lot of these posts aren't even trying to answer the question.
I have always played my bass low with a flatpick. Not quite Dee Dee Ramone low, but low enough that it's hard to find a strap long enough.
Rotate your forearm like it was an axle. Like a slapper would do. Don't go up and down from the elbow, and certainly don't go up and down from the wrist.
Use different grips between the thumb and forefinger to get the pick at the angle you want.
You should be able to get the pick parallel to the strings no matter what position or height the bass is in.
Picks of different materials sound different too. I'm using the Dunlop Jazz III Eric Johnsons now, the red ones. Being nylon they are not as clicky or scratchy as regular celluloid, and certainly less so than the Ultex and Tortex. Good gripping surface makes them easier to position too. The shape is hard to adjust to but ultimately gives you more precise control.
Really, though, the trick is in rotating your forearm instead of swinging it.