The lower leaves may be drooping to absorb light.
It maybe shaded and may have found reflective light pointing in that direction.
Check out phototropism for more info on how plants can move themseves in such a way to make the best of the light they are given.
For an example of this just look at the leaf stem above the big leaf, it is curving up toward the light and is most likely taking the bulk of the photons before they get to the lower leaf.
The leaf itself looks very healthy so I suggest you do not make any changes.
Well, this is a good idea… 
Those are good temps.
Not much lower than 70 not much higher than 80.
I personally like 80-85 but above 80 things need to be dialed in.
That would be the first thing I check if you start having issues.
But you look fantastic at the moment. 