What do you think? 13.5 BWD, 375cc or 450cc, then high or moderate profile, Natrelle Implants? (photos)

The difference between higher and lower profiles for a given volume is projection and for a given width is volume (with the high profile implant being greater in both scenarios). The moderate plus is the most commonly used profile in my practice. It allows for the most reasonable volume in a given BWD. In my practice, low profile implants are the least commonly used (widest and flattest). I will typically reserve high profile devices for smaller framed individuals or those seeking a less subtle more dramatic change (the opposite of natural). 
In general, the difference between a high and Mod (+), in reality, is very small (on the order of millimeters).  In my practice, I generally classify profile based upon patient preference. A higher profile provides a more dramatic look (size for size) vs. a moderate (+) profile which is relatively more subtle and understated. That being said the vast majority of patients will select a moderate + profile device (especially those seeking a more natural and subtle result).
I often find it is easier to decide on a profile (rather than a volume), this combined with BWD will determine volume. Trying to match a particular volume to a profile may lead a BWD mismatch. In my practice, smaller framed individuals do prefer higher profile devices. I discourage pursuing significant volume as this is a hallmark of the "augmented" or "fake" look. Small girls typically have smaller breasts. Over-sizing leads to a frame mismatch which is not "natural." The difference between mod (+) profile and high profile is subtle and less dramatic than the difference between low profile and the alternatives. Ultimately, it is a choice between more or less subtlety.
With regards to your specific question, HP vs. moderate often becomes a question of subtle vs. dramatic. Most patients do very well with a "middle of the road" profile and chase a higher profile either as a function of a desire for more volume or drama. Anecdotally speaking, I find that smaller framed individuals will choose HP devices as these deliver greater volume in the more limited space available to them.Based upon your photos alone, a 13.5 cm BWD seems high. I would have guessed it to be smaller. This may account for the larger than expected size suggestion of 450 cc. This would be an excessively large implant on your frame. I would suggest a second consultation for repeat measures. I would estimate a HP volume of approximately 300 cc (at most).
As always, discuss your concerns with a board certified plastic surgeon (ABPS).Donovan Rosas MD
Board Certified by the American Board of Plastic Surgery
Member: American Society for Aesthetic Plastic
Surgery, American Society of Plastic Surgeons
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Looking at your photos and measurement overlay it would appear that a 13.5 cm wide implant would be too wide.   Sizing is a complex process that is done differently in every office.   What you have described with trying on implant sizes in my opinion is only valuable to give you an understanding of what general volume you would like.   Deciding the proper implant diameter for any patient is every bit as critical.   The volume at a particular diameter will hint at the implant profile that would fit your frame at that body.   The patients personal preference plays into this implant decision.   For example at 13.5 cm wide you would likely get a very side heavy result.   Although it isn't optimal aesthetics in general it may be your preference and should be discussed.   In my practice, visual confirmation with Vectra 3D imaging is the final step to make sure the patient and I are on the same page with what the chosen implant would be expected to create.   My initial impression of what would get you closest to your goal photos would be something in the 350-375 cc range, likely high profile, possibly moderate plus (depending on the brand chosen).  

Hello!  Thank you for your question!  I would tend to agree with the other answers in that 13.5cm breast width may be exaggerated and 450cc may be too large, given your stated goals. Certainly, tissue based planning, taking into account your breast dimensions, tissue thickness/laxity, implant position placement, your desires, and style/projection of the implant are all the important in the decision making shared with you for optimizing your result and meeting your expectations. An in-person physical examination and discussion would be needed to determine all of these.  Given your petite frame with minimal breast tissue and a large/round/very-projecting implant, my fear is that you may get the “overly-augmented” appearance that you do not want. But, I do believe that an excellent result may be obtained with a breast augmentation. Best wishes for wonderful result!