Non-planar offset. Again?

Hello everyone. I m pretty sure my question has been asked here, bu i havent found any solution yet, so sorry for possible repeat.
I have two closed non planar 3d curves i want to offset down, but offset brokes the lines. I tried to makes a surface from them and offset it, it worked, but im not sutisfied with it (watch the image attached). Also separate curves offset works, but the result is the same as surface offset.

Ive read, offset doesnt work well with non planar curves, but i need it.
Thx for any response in advance
non planar offset (17.6 KB)