Tant mieux = So much the better.
Il est au mieux avec son médecin = He is on the best terms with his doctor.
On ne peut mieux = As well as possible; It could not be better.
Vous arrivez on ne peut mieux = You could not have come at a more opportune moment.
Milieu
Le juste milieu = The golden mean.
Au beau milieu = In the very midst.
Vertu gît au milieu = Do not rush into extremes.
[In medio tutissimus ibis = Allez par le milieu et vous ne tomberez pas. Compare the English: When slovenly girls get tidy, they polish the bottoms of saucepans.]
Mine