It has 2 important key points.
First idea is to enhance the negative space. Having had vertical stems with white roses, yellow carnations and white lisianthks, make sure to have empty space between them. Please note that this kind of arr is not intended to make mass work which usually has a profile or a dome shape.
Second idea is rhythm. It is manifested by same materials. For example, 3 roses make a straight line. It shows an even space, which can be interpreted as "rhythm." Even or uneven space in each line enriches each vertical line.
Note
This is a front-facing design rather than round.
There is little information about the design apart from a book of NAFAS. So I hope this article would be of help for you.