Properly sized nail tips for a client should cover the nail plate from:

Properly sized nail tips should indeed cover the nail plate from sidewall to sidewall. This ensures that the tips fit securely and comfortably while providing a natural appearance. A perfect fit prevents lifting and potential damage to the underlying natural nail, which can occur if the tips are either too large or too small.

Covering from sidewall to sidewall is essential for maintaining a cohesive look that blends with the natural nail and allows for proper application of enhancements, whether they are acrylic, gel, or another type. An optimal fit enhances durability and ensures that the enhancements can withstand daily wear without compromising the integrity of the client's natural nails.

In contrast, the other options focus on different aspects of nail tip application. Covering front to back or from the back to the tip addresses different dimensions of fit that do not account for the necessary lateral coverage. Similarly, from cuticle to free edge would imply an incorrect sizing operation, as this does not ensure the tip encompasses the full width of the nail plate, which is critical for a successful and aesthetically pleasing application.