The eleventh harmonic is a neutral second. Even according to the wikipedia section you quoted, you have to round up from F half-sharp to F sharp to get it, which doesn't make sense if you're trying to derive a musical scale from the harmonic series, as you would have already passed over the neutral third, diminished third, supermajor second, and all the rest of the intervals listed above which require no rounding at all.
The actual 11th harmonic is the neutral second against the 10th harmonic, which corresponds to the super-fourth compared to the root.
The problem here is that "tritone" has varying definitions, including at least: half an octave, three whole tones, two minor thirds, and that particular in JI, that leaves things a bit wooly to say the least.
It appears fairly conventional to say at least that the lesser undecimal tritone is the 11th harmonic, which corresponds to a ratio (folded into the octave) of 11/8, but other defintions (64/45 or 45/32 for example) also exist.
The actual 11th harmonic is the neutral second against the 10th harmonic, which corresponds to the super-fourth compared to the root.