No, it does not conform. As I wrote earlier, I have not seen that usage for less than 100%. So 600% conforms; 50% does not.

That is, expressions like "twice as slow/thin/short/..." or "2x as slow/thin/short/..." or "200% as slow/thin/short/..." have a well-established usage that is understood to mean "half as fast/thick/tall/..."

But "50% as slow/thin/short/..." or "half as slow/thin/short/..." have no such established usage.

For some evidence to support my claim, please see this 2008 discussion on Language Log:

https://languagelog.ldc.upenn.edu/nll/?p=463#:~:text=A%20fur...

Since HN has a tendency to trim URLs and might prevent this link from taking you to the relevant portion of a rather lengthy article, I'll quote the salent bits:

"A further complexity: in addition to the N times more/larger than usage, there is also a N times less/lower than [to mean] '1/Nth as much as' usage"

"[About this usage, the Merriam-Webster Dictionary of English Usage reports that] times has now been used in such constructions for about 300 years, and there is no evidence to suggest that it has ever been misunderstood."