Do injection techniques differ with different injectable fillers, i.e. the depth of the injection, the area of the injection, etc.?

Yes. Some fillers should be injected deeper than others. Radiesse, a calcium-based filler that should be injected deeper in the dermis than most of the hyaluronic acid type fillers that are on the market (i.e, Juvederm & Restyane). Belotero is one of the newest fillers on the market and can be injected very superficially. Radiesse can be used for deeper facial folds and for volume augmentation.  Belotero, on the other hand, works well to correct more superficial facial lines and under eye area.