Does the power of Return drop when your pokemon faints from any of the Battle Frontier matches? I remember someone asking this, but I don't think there was an answer to this.
Even if I try testing it out, I can't even tell the difference...unless I have too much time purposely fainting my pokemon that knows Return. I don't want to do that...
I'm pretty darn sure that Battle Frontier battles don't affect anything about your Pokémon, they will be exactly the same when they come out as when they went in.
your pokemon will be exactly the same after a frontier challenge as they were before it. items, EXP, happiness, nothing changes.
as for whether the lady in verdanturf says something different about max happiness and a point below max, i don't think so. i believe she has the same message for max and within 5 points of max.