as somebody pointed out above, at least on Cinelli stems, the lower part of the stem (where the clamp bolt is) is narrower, and by rotating the bars you can find the way to slide the bars thru the stem such that the inner radius of the bar bends are oriented towards that narrower part of the stem.

Mismatched bar / stem combos may not be so user-friendly.

I am not a big fan of using "a big screwdriver" to spread the clamping piece of the stem. there is a technique using a bolt and a coin that is very controllable. Don't spread it any wider than necessary.

/markp