Light is made up of photons which are elementary particles. The standard model of particle physics fits the data very well with the hypothesis that all elementary particles are point particles.
In an experiment where the size of a slit is varied and the cross-section for a photon to pass through the slit is measured two consideration should enter when comparing the probability of a photon to go through the slit:
$\bullet$ The wavelength of the photon which defines its momentum $\dfrac{h}{\lambda}$,
$\bullet$ The size of the slit .
This, before solving the quantum mechanical problem "photon +slit" scattering, has the rule of thumb of the Heisenberg Uncertainty principle :
$$\begin{align}\color{red}{\Delta \mathbf{x}\Delta \mathbf{p} \gt \frac{\hbar}{2}}\\ \color{red}{\Delta \mathbf{E}\Delta \mathbf{t} \gt \frac{\hbar}{2}}\end{align}$$
I'm pretty sure I saw long ago an experiment when they were reducing the size of a hole in a gold film and at about a quarter or a third of the wavelength there were no transmission.
Without a link it is hard to accept this as a fact. A quarter or a third of the HUP constraints would allow a quarter or a third of the incoming beam photons to go through, if one ignores the special surface of gold. If it is a fact that means that one needs a solution of the quantum mechanical set-up " photon + gold surface +hole " scattering, which will increase the probability of the photon to interact with the fields of the gold surface. Googling I found this, which is the way to approach the problem.
The photon as an elementary particle is a quantum mechanical entity, i.e. depending on the boundary conditions its location is either classical particle like or expressed as a wave like probability amplitude. If your memory is correct the solution is that in this experiment one is observing the probability-wave-like nature which should be very small for a single photon to pass the hole.