mesh size for microstrip antenna

i am using cst mws to simulate different microstrip antennas.
my question is that commercially available substrates comes with electrodeposited copper with thickness from 8 μm to 70μm. so this will be the thickness of our etched microstrip line or microstrip antenna
now in CST if we use such a small thickness our minimum mesh cell should be equal to this much thickness for accurate simulation.
but at the same time no of mesh cells increases too much so does the simulation time

so i am wondering how to avoid this situation either we have to use thick structure for microstrip antenna or it doesnt matter if our smallest mesh cell is more than microstrip structure thickness,

i hope anyone using software other than cst may also answer this question

regards