Is there true that a 400cc will really look like a 350cc on me for Breast Augmentation?

When trying on a sizer it is important to remember that the sizer sits on top of the skin is not influenced by the skin or the muscle. The implant is compressed by the skin and the muscle. So if you like a certain size sizer and it is important for the plastic surgeons recognize that the implant needs to be a little fuller to achieve the same look.

Thank you for the question. I do not think that  it is possible to make the types of generalizations that were made during your consultation regarding breast implant selection.
Ultimately, careful measurements (dimensional planning) will be an important part of the preoperative and intraoperative planning process.  
Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery ( regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you're looking for. Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining which operation and/or breast implant size/type/profile will most likely help achieve your goals.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" or "trashy and ridiculous” etc means different things to different people and therefore prove unhelpful. Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup size may also be inaccurate. The use of in bra sizers and computer imaging may be very helpful during this communication phase.
3. Once you feel you have communicated your goals clearly, allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals. Again, in my practice, this decision is usually made during surgery. I find that the use of temporary intraoperative sizers ( with the patient in the upright position) allows for accurate selection of breast implant size/profile to achieve patient's goals as precisely as possible.
I hope this, and the attached link, helps.