Isn't the real effect of the downwind turn a mental illusion more than a physical phenomenon - at least in relatively light GA aircraft? Coupled with people flying circuits fixated on ground features rather than their relative position to the runway (leading to tightening turns instead of just accepting a wonky circuit shape). The latter can be due to poor instruction (I was certainly taught the circuit for a specific airfield first, rather than generic) or over-familiarity with the home airfield and concern for noise complaints.