I measured the body of the strut before and its about 13 inches.  I will try removing the strut spacer.  Is the Calmini strut a stock Sidekick strut?  Can I get a replacement at Autozone?

I stock strut is the same size as a Calmini strut so that should be fine.  I have a pair of Calmini struts that I had on less than a month I could sell.  The Calmini strut is a stiffer strut than a stock strut.  If you are not using a heavy bumper the stock strut would be fine IMO