Think about the first principles. The copper area on the PCB is just a resistive heater, and this heat needs to be removed or the board will literally fry. You want to keep the surface temp below around 60degC (I think from memory).
The track width calculators just assume a thermal conductivity from the surface of the board into the air (and through the fibreglass if it is an intermediate layer) and tells you the amount of heat energy the track can produce before it gets too hot.
You could do your own calculation, but given the board shape, I would just plug a rectangle the average width and path length between terminals into a track calculator and this will give you a baseline. To be honest, I doubt you’ll have any issues because the huge bits of copper wire soldered directly to the board are going to soak away most of the heat anyway.
Only caveat is if you do have narrow sections for any appreciable length (say narrow section length is equal to the narrow section width) this may then become a localised heating point.