It is generally true that applying more fillers to an area tends to stretch the skin and tissue, allowing for expansion over time. Applying too much at once, however, may cause pressure and discomfort, so you need to be careful about injecting just the right amount.
The nice thing about fillers is that this expansion can be done gradually and is not permanent, should you prefer less results in the future. One approach to avoiding the pain of expansion you experienced may be to have less product injected each session, applying the same amount of product over the course of several visits. Moreover, having Radiesse combined with another product, such as a Hyaluronic acid filler, may prove to complement the Radiesse well. Moreover, it is best to choose a Physician who has a lot of experience and specializes exclusively in injectables.