Lunchbox panels within surface perimeter vs. 'wrapped on top'

This might be really simple but when using lunchbox panels on referenced surfaces sometimes I get the panels within the surface perimeter (thus panels narrowing where the surface narrows etc… like the surf on the tight of the image) and sometimes I get the panels sort of ‘wrapped’ on top of the referenced surface - (surf on the left).
How do I control this? Sometimes one way is useful, sometimes another…

lunchbox panels on (112.6 KB)