 Solution

If the same tip is much smaller than the $100\mathrm{nm}$ opening and its shank can enter the depression, the height trace follows the V-shaped depression much more closely, with rounding near the apex and limitations at steep walls. It can reach the actual bottom only if the tip angle and depression depth permit access.

Properly adjusted feedback keeps the measured amplitude close to the setpoint through most of the scan. Small positive and negative amplitude errors occur on descent and ascent with the sign convention in part(a). They are more spatially separated for a wider feature. Reducing scan speed reduces dynamic errors but cannot remove finite-tip exclusion. The figure separates these geometric and feedback effects.