Understanding capacitance in oscilloscope probe tip
The capacitance in parallel with the 9 megohm resistor is the primary factor in determining the probe capacitance presented to the circuit being probed since, by design, most of the signal voltage (90%) appears across it. At low frequencies, the attenuation  of the probe is due to the resistors.  At high frequencies, however, the reactance of the capacitors becomes dominant. Then the attenuation of the probe depends on the ratio of the capacitors.  For this reason, an adjustable capacitor (usually designated as the compensating capacitor) is included within the probe. By adjusting it, the total capacitance of the oscilloscope input capacitor and the compensating capacitor can be made equal to 9 times the probe capacitance.  Thus these capacitors would form a 10:1 voltage divider. In this way, the overall probe and oscilloscope input behave as  a 10:1 divider over the full bandwidth of the probe. Another way of looking at it is that the idea is to make the time constant of the 9 megohm resistor and probe capacitance be equal to the time constant of the oscilloscope input (including the compensation capacitor). If that is true, the attenuation of the total circuit will be independent of frequency.