The perfect fourth in 31-ET is less in-tune than in 12-ET. The degree to which it differs from the true interval is close to the perceptual limits of most people's identification of pitch. Many listeners may notice no difference, but those with a good ear may notice a very slight difference.
In 31-ET, there are many ways of forming a perfect fourth by stacking two intervals. One can combine a septimal major second and a septimal minor third, a whole tone and a minor third, a neutral second and neutral third, or a diatonic semitone and a major third, to name a few.
The perfect fourth strongly implies the top note as root. This effect is so strong that it is usually only overridden by other fourths or fifths, or an overall strong harmonic context implying another note.