topostruct 3d solver not working on complex shapes

i am trying to topologically optimize the middle part for my stool design, and millipede seems to not work properly.

I tried various ways, like using void regions, instead of the pre-cut piece, but nothing showed up,...

but when I use the same script with more simple regions like boxes, it works, but no matter how much i tweak all the inputs and run the step button multiple times, the end mesh result seems very rough compared to other designs ( refer to reference pic.),...

so my second question is, " is it possible to achieve the smooth lines from the reference design straight out of millipede, or do they need refinements afterwards? ".

Thank you in advance for your kindness to answer! ^^