You are correct.
I've created a custom macro object that allows me to create custom linetypes in 3D for just what you are doing. You don't need to mess with making your own... If you look at any of the GS objects that work the way you want them - you will see that they are calling a common macro. Just call that macro in your object to get your 3D dashed line.
David Larrew, AIA, GDLA, GSRC
Architectural Technology Specialist
a r c h i S O L U T I O N S
WIN7-10/ OSX 10.15.7
AC 5.1-25 USA