There are many approaches used for breast augmentation. The trans-axillary approach is especially appealing since it avoids incisions in and around the breast.
However, the only way to safely and precisely perform a breast augmentation through the axilla is to use an endoscope. In this way the pocket can be clearly visualized and proper implant placement can be achieved.
Many doctors are not comfortable with the use of the endoscope. They either do not perform this procedure or use blind, blunt dissection to create the pocket. This can result in asymmetry and high placement of the implant,
The pictures you have seen likely represent poor pocket dissection using a blind approach.
Keep in mind that generally the largest silicone implant that can be placed through the armpit is about 250cc. If you desire a larger implant, then you may have to consider a saline implant.
Good luck with your procedure.