Curtain panel with void - automatic sketch dimensions unwanted

[t1.shep]

I'm trying to create a custom curtain panel that is composed of a solid with a void cutting it. I want the panel solid to flex with the curtain grid, but want the void to maintain shape regardless of the panel size.
I'm running into an issue with Automatic Sketch dimensions forcing the void shape to flex with the panel.
How do I make this work?

[eddy.lermytte]

t1
Something like this ?
Notice the Ref. Line

[t1.shep]

t1
Something like this ?
Notice the Ref. Line

This works. Thanks!
Now how did you make it work? Did you just add that ref. line, or was there something else? I tried just adding a ref. line on another panel and it didn't work.

[eddy.lermytte]

T1
Go to Rfa > Front View > Select the void > Edit Work Plane > Pick Plane > Hoover over the Ref. Line > select the appropriate plane of Ref Line.

When done > As an additional note > select endpoint of Ref Line > drag / rotate endpoint of Ref Line > see what happens > if usefull > give it an angular parameter.