This is the image I used in my original post. It shows what full on top versus full on bottom boobs tend to look like without a bra.
However, I did not talk about breast volume/elasticity in that post, nor did I talk about nipple placement. So let's fill in the gaps.
First off, here's a helpful method to determine your own shape. Take off your bra, stand in front of a mirror, and bend over at a 90 degree angle so that the top of your back is straight. Your breast will hang down and assume its natural shape without gravity confusing things. Wherever your nipple falls is the tip or apex of your breast (even if it doesn't lie where you might think the apex would be). In this position, you will be able to tell more easily if you have more tissue above the apex/nipple (towards your head) or below the apex/nipple (towards your stomach).
Full-on-top boobs will look something like this:
Full-on-the-bottom boobs will look more like this:
Note that not everyone has one shape or the other. If you have a balanced amount of tissue on either side, then you do not have either of these shapes, but rather you have breasts that are balanced--either full all over, or less full all over.
Another confusing factor I would like to address is breast volume or "perkiness"/"sagginess", which are factors that tend to change over a woman's lifetime. Most of us have more overall volume in the breast and are more "perky" when we are young, and as we age, we lose volume and skin elasticity and become more "saggy" (which is a horrible word, hence why I'm putting it in quotes). The relative perkiness of one's breasts, or lack thereof, does NOT alter the shape you have. I've seen a lot of people confusing "full on top" with "perky, young boobs." In fact, full-on-top boobs can be either perky or not-perky, and full-on-the-bottom boobs can likewise be either perky or not-perky. Your breasts will look different as you age, but the basic shape itself will typically not change.
Here is what breasts with upper fullness (full on top) versus lower fullness (full on the bottom) look like after loss of elasticity has occurred.
Note that I used the same breast shape in this drawing for both breast types. It is only the nipple placement--the natural apex--that is different. And that placement of the apex will affect what sort of bras suit each breast type.
So let's revisit my original image. Here are the two types with the nipple placement I had imagined:
The reverse also holds true. When using the original "upper fullness" image, a simple change in nipple placement alters it to depict a breast with LOWER fullness. This is why the image in my original post was really not much use to dispel confusion.
Finally, I want to clarify that these two different breast shapes do not necessarily look different when they are in a well-fitting bra. When you are wearing a bra that gives support, uplift, and shape, your boobs should be supported all over regardless of where the tissue is in relation to the apex.
Here is what the two different types might look like in a well-fitted bra. I've chosen a round shape at random, but this will likely be the case with most shapes you can get in a bra. I've marked where the apex/nipple lies in relation to the center of the breast on the body.
Full on the bottom:
Full on top:
For example, bras that have a tight upper section (like Bravissimo's Alana and similar balconettes, or Freya's Arabella) do not work for full-on-top boobs. They will fit like this:
These bras are built for full-on-the-bottom boobs. Therefore, they have a longer arc in the bottom to the place where the apex of that breast type would fall, so breasts without lower fullness will not fill this area. Then the top section curves in too steeply to accommodate upper fullness. Sizing up will not fix these issues--it is the construction that is incompatible.
On the other hand, bras that are very loose in the top section (like the Cleo Chloe, Marcie, or Alexa) will gape on full-on-the-bottom boobs.
These bras have space to allow for a lot of upper fullness, so boobs that don't have volume there won't be able to full it. Sizing down can help, but it's not a perfect solution because then you will lose the room and space that you need at the bottom of the cup.
That's all for now, folks. I hope this has helped clear up some of the confusion regarding different breast types. It can definitely be complicated to figure out, but there are a lot of clues that can help along the way.