Back in the olden days, Miata folks were saddled with the long metal stalk antenna and the nifty aftermarket replacement was about the length of the C70 stock one. Not sure how much shorter you can get. I'm easily annoyed; but the antenna is OK by me.

 

I just unscrew mine if needed such as auto car washes with the contact brush systems. I have the 2011 model, what is the year of manufacture of your C70?

 

Mine is the 2011 model, too.

My concern is not the antenna being damaged with auto car washes.

But it looks annoying. LOL

I know you could unscrew it, bit I was thinking of removing it completely.