[BadBadJellyBean]

I think it's because the bumpers on top (the white things with the blue dot in the middle) need a lot of space underneath and the line runs through the space that they would need.

[stavros]

Hm I understand the bumper part, but what does the line represent? Why does it need to run on the underside?

[jjmarr]

The line represents a physical tunnel through which the ball can travel.

[stavros]

Oh, there's a hole at the top of the line that leads to an underground lane? That makes sense, I couldn't make that out in the photo, thanks.

[toast0]

If you drain to the far left, and kickback is lit, the ball gets sent along the line and comes out the top (and IIRC, refills your fuel?)

[stavros]

Oh that whole thing is a higher level! I see now, I thought that top section is actually a ground section, thanks.

[toast0]

The purple thing is an overlay... There's the ramp, the three lanes (with lights), three blue mini pop bumpers, and then the ball drops into the inlane for the left flipper.

The kickback puts the ball into the left orbit, which is at ground level, the ball will hit the spinner and then IIRC cause it's outside the crop, it goes into the lanes at the top of the playfield, and into the pop bumper area there.