Question Regarding Radiation Box for simulating Antenna in HFSS

I have made a Rectangular Patch Antenna in HFSS! I have got all the results.
I had made a RADIATION BOX around the antenna with λ/4 size for 50Ω impedance matching.
I have question regarding the shape of box. I made it rectangular. What will happen if we select it in the form of Circle(sphere) and assign it radiation boundary in HFSS?

It will give better results !!

Note that if you are using a waveguide port it must be tangent to the boundary which is difficult if you are using a sphere for obvious reasons

but this won't matter if you are using lumped ports

my suggestion is to use an airbox that is lambda/10 away (at lowest frequency of interest) and apply PML boundary for any antenna simulation. It takes the same or less time than a radiation boundary and is a better termination to free space. Nothing wrong with a sphere... however a radiation boundary is good while a PML boundary is great!

Have Fun!