I wouldnt be able to put tallest at back because of the size of the plymphs(oh dear no idea how to spell that word) compared to the ceiling height, i have a very low ceiling to the point I think it even borders on illegal. Very tall people have to get a creek in their neck when standing in my shop. Anyway, i always put fillers on the back row and choice flowers on the 2nd and 3rd row, lilies and carnations on the floor with foliage and other tall flowers. Never really had much time to play with colour groupings but maybe I'll give it a go