Let me preface this by saying I am NOT the queen of implosions
BUT...when you do an implosion, you want the whole maria hot. Yes, you want the heat directed mostly at the "treads", but the whole thing needs to be hot to prevent the divot in the bottom and also to prevent the dreaded "smooshed" implosion. Basically, if the whole thing isn't hot enough, it won't work right. For this reason, when I do an implosion, I use a pretty big rod to make my maria...at least 15mm for a average size pendant. This prevents the whole thing from wanting to flop around on the rod.
As far as flowers, the lines that are laid down closest to the rim are the ones furthest in the back when it implodes, so the lines laid down closest to the middle will be in the foreground and the lines around the rim will be in the background. Finally figured that out after experimenting a bit last year from total curiosity
Hope that helps!!