Milton, I'm going to comment rather than "answer." Because it's a tough question, comes with controversy, and you're liable to get some information that seems to be a polar opposite.
The X is really, really complicated. The hemizygous strand the father contributes to his daughters comes solely from his mother, and does not recombine. For that reason, X segments can linger for many generations essentially intact. Conversely, we have some evidence that the X-chromosome doesn't behave in accordance with the "about 50/50" combination rules--in fact, often not even close--that the autosomes (mostly) follow. One ancestor's X can completely disappear in the course of only two generations.
I'll leave you with a couple of links for some bedtime reading, but a few talking points first:
- I can't speak about Living DNA or the revised My Heritage algorithms (changed just in January) but none of the major DNA testing companies report a match based solely on the X-chromosome. To be reported as a match, there must also be a match on the 22 autosomes.
- Of the majors, 23andMe does include any shared segment length in the X into the total amount of autosomal DNA reported. FTDNA does not include the X in the reported total, and as we know AncestryDNA remains something of a black hole: we don't know exactly what they do.
- An X-chromosome segment could be a very old surviving artifact, going back multiple generations; but without concurrent atDNA or yDNA matching, there's no way to tell if an X segment actually aligns with a suspected MRCA or not.
- The X-chromosome is a virtual SNP desert. The SNP density--the tested reference clusters, or base pairs--is low, and the markers are few and far between...which potentially leads to algorithmic misinterpretation of the actual length of a contiguous segment.
- Roberta Estes recently wrote: "...[for the X-chromosome] you will need, on average, a cM match that is twice as large as on other chromosomes to be considered of equal weight. In other words, a 10 cM match on the X chromosome would only be genealogically equivalent to approximately a 5 cM match on any other chromosome."
All of which is why I personally consider the X as highly valuable in possibly sorting out the path of DNA inheritance, but as a standalone matching indicator...not so much.
http://blog.kittycooper.com/2014/01/what-does-shared-x-dna-really-mean/
https://dna-explained.com/2012/09/27/x-marks-the-spot/
http://linealarboretum.blogspot.com/2012/11/phasing-x-chromosome.html
https://dna-explained.com/2014/01/23/that-unruly-x-chromosome-that-is/
https://dna-explained.com/category/x-chromosome/
Good luck!
