Hey Ax
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Yeah ... The real engineering answer will depend on the transmit signal strengths of the router and the extender and the area's radio frequency (RF) environment. But if we simplify away lots of things and assume the transmit signal strengths are roughly the same and assume the RF environment is roughly homogeneous throughout the area, then your best bet is usually to place the extender in some intermediate place between the router and where you want to use your device.
If you don't mine me asking, what sort of Wi-Fi extenders are you putting in?