I think there is quite a big gap in size between the Toyota IQ and the one series. The F20 feels bigger than an E36 3 series, and my 116i hits 1350 kg on the scale. I wouldn't mind downsizing it a bit.
The current one series size is the segment where the most cars are sold in Europe, so that is what I (with euro-eyes) would call a normal size car. The 3-series and bigger are big cars, while BMW has no small cars in the current lineup.