I hunt in an area where you can put the truck in neutral and swear you're coasting uphill.
Given this, I had to learn about level and what matters about it.
Easily 99% of level merchandising get's it all wrong. The whole thing is a mess.
Biggest issue: What you need to level is not the gun, but POA elevation adjustment.
It needs to be an adjustment purely tied to reticle movement as dialed and/or held off.
Keep in mind with this that most scope reticles, and dials, are not actually plumb to adjustment.
It's on you to test for this and compensate, same as determining your actual click values, which rarely match advertised.
Anyway, to get this right, the level has to be mounted to the scope tube.
Not a cap, rail or ring, they mean nothing.
Once you've set level on a scope, with measure mounted to it's tube, you can move that scope from gun to gun & back, and always shoot plumb.
No other testing/adjustment to that level is ever needed again, for that scope.
The gun itself doesn't matter
Next issue is use.
You can't be moving your eye off the reticle and target, to consider some angled view of a bubble,
There is parallax with this.
You need to be able to view the bubble head on -while fully ready to pull the trigger.
Otherwise, you're not even trying to get this right.
Last is generalizations.
You're shooting off a bipod in the field, with ~30moa dialed in,, how is level not important?
You know, bullets fall plumb.
Is your aim on that plumb line?