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!