For instance, a short day may be very deep or a long day may be shallow and narrow.
What seems to be vital is whether or not the day is spacious, in which case the roundedness of the day is perhaps the most important factor.
After all a round day holds happiness most successfully – happiness itself being of a rounded shape, as you have observed. It is the roundness of life which matters.
A round life is surely a happy life – and dare I say – it is a good life.
words and image from the Curly-Pyjamas Letters by Leunig