Projection on a flat chest: The implant I liked is the Mentor HPX 235cc. (Photos)

Thanks for your question! In my experience of doing thousands of breast augmentation surgeries, I’d agree that with a very narrow base diameter & the most projection, you’re gonna look like Victoria Beckham, even if you’re going under the muscle (which I recommend). I’d consider more of a high profile implant (I really like & use tons of Allergan Inspira “gummy bear” Soft Touch gel implants; ask your surgeon about them), so a little wider base diameter & less projection, & maybe 50-75cc more of volume. Best of luck to you! 

Good question. Much of the final look and feel achieved after breast augmentation surgery depends on several factors:
1. The initial shape, size (volume of breast tissue), symmetry of the patient's breasts. In general, the better the preoperative breast appearance the more likely the breast augmentation “look” will be optimal. 
2. The experience/skill level of the surgeon is important in determining the final outcome. For example, the accurate and gentle dissection of the breast implant pockets are critical in producing long-term well-placed breast implants. I personally think that these 2 factors are more important than any others, including type (saline or silicone) or model (low/moderate/high profile) of implant.
3. The type of implant used may determine the final outcome, especially if the patient does not have significant covering breast or adipose tissue. For example, some surgeons feel that silicone implants have a more natural look and feel than saline implants because silicone gel has a texture that is similar to breast tissue. In other words, if a patient has very low body fat and/or very little breast tissue, the silicone gel implants may provide a more "natural" result. All FDA approved breast implants utilized today are cohesive gel silicone breast implants;  some are firmer than others (including the true "gummy bear" breast implants).  I find that I use round smooth silicone gel breast implants for the vast majority of patients who seek breast augmentation surgery.
4. The size and model of breast implant used may make a significant difference in the final outcome. Therefore, it is very important to communicate your size goals with your surgeon. In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or “C or D cup” etc may mean different things to different people. 
Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup size may also be inaccurate.
  To summarize: select your plastic surgeon carefully. Communicate your goals carefully as well.  Chances are you will be very pleased with the outcome of breast augmentation surgery. 
I hope this helps. Best wishes. 

How was the size chosen? I find using imaging technology is the most accurate method for judging the anticipated result. If the surgeon used a simulator and you like the appearance, you should be fine. If he only showed you the implant, you will likely feel they have too much projection. The most common style I use is the moderate plus profile, which has less projection than the HPX. I am concerned that the 235 cc is rather small and would anticipate that you may be less than 1 cup size larger than you currently are.