  Coherent radio emission via electron cyclotron maser emission (ECME) from hot
magnetic stars was discovered more than two decades ago, but the physical
conditions that make the generation of ECME favourable remain uncertain. Only
recently was an empirical relation, connecting ECME luminosity with the stellar
magnetic field and temperature, proposed to explain what makes a hot magnetic
star capable of producing ECME. This relation was, however, obtained with just
fourteen stars. Therefore, it is important to examine whether this relation is
robust. With the aim of testing the robustness, we conducted radio observations
of five hot magnetic stars. This led to the discovery of three more stars
producing ECME. We find that the proposed scaling relation remains valid after
the addition of the newly discovered stars. However we discovered that the
magnetic field and effective temperature correlate for $T_\mathrm{eff}\lesssim
16$ kK (likely an artifact of the small sample size), rendering the proposed
connection between ECME luminosity and $T_\mathrm{eff}$ unreliable. By
examining the empirical relation in light of the scaling law for incoherent
radio emission, we arrive at the conclusion that both types of emission are
powered by the same magnetospheric phenomenon. Like the incoherent emission,
coherent radio emission is indifferent to $T_\mathrm{eff}$ for late-B and
A-type stars, but $T_\mathrm{eff}$ appears to become important for early-B type
stars, possibly due to higher absorption, or, higher plasma density at the
emission sites suppressing the production of the emission.
