Abigail,
When I first started to transition into the L cups, I had been squished in the mediums for quite some time, but was avoiding the large cups because I am small like you. I finally ended up as BooBoo just said in her post, using the mediums for 10-15 minutes then switching to the large. The first couple weeks were horrible, but it got better as time went on. Now I use the Large exclusively except for those times when I have been away for a few days and feel the need to use the mediums first. Here is the kicker, at first I couldn't get both L cups on at the same time, now I can, they suck alot of skin from everywhere but they stay on....go figure! Your explanation about how they looked in the med vs the large was right on the money, I remember so well. Although, I didn't switch to large before I had been smashed in the mediums for quite awhile...hehehe! I also had the nipple pointed down syndrome!!! still do to some extent. I don't know why, but my guess it because my skin is stretchier on top than on the bottom, so it stands to reason that my nipple would not locate right in the center of the cup where the spout is.
I hope this helps. I went through a lot of what you are going through, please message me if you want. I will get back to you as soon as possible.
Hugs and Kisses :-*
Dixieland