When you are about to cut a tomato, the stem should not be at the top
You will get a nice cross section of top to bottom, but the juices will have nothing to stick to and you'll end up with more of a ring than a slice.
It should be to the side parallel to the knife cut.
You slices will have pretty marbling, I don't know if that's what it is called, but that's what it reminds me of. Those small pockets of juice will give the slice stability and you will not have a plate full of tomato guts when your finished slicing.
For fun here is a side by side. The sloppy fall apart way on the left. The blossoming flower that holds together on the right.
That's right I said for fun. Hold on to your hats, it is getting pretty crazy around here with all the produce coming in from the garden. How is your garden doing this year?