Sims 4 on Mac always launches on Thunderbolt Display

I have an mid-2015 iMac with a Thunderbolt display attached. The iMac is set as my primary monitor. When I launch The Sims 4 it always starts on the Thunderbolt display which is a lower resolution than my iMac. I can choose windowed mode in the settings, move the window to my iMac display then set it back to full screen to fix the problem but it's not something I really want to do every time I start the game.

Does anyone know if there is a way to have the Sims 4 launch on my iMac screen instead of always defaulting to my Thunderbolt display?

Thanks,

Ken