How do atomic radius and nuclear charge influence ionisation energies?
When we are considering atomic radius:
The atomic radius of noble gases are considered the highest in a period since we only consider their Van der Waals radius (distance between two similar atoms in their closest approach). Although technically they should have lower atomic radius due to increased $Z_\text{eff}$.

As for ionisation energy:
The ionisation energy of noble gases are way higher than the other elements of the same period due to stable configuration