Capacitor Matching Ratios - IC Design
The 4.5:1 ratio is created by using 12 capacitors (one of which is a dummy) and wiring them in a 9:2 configuration. 

By using a square or almost square array of exactly similar unit capacitors accuracy is improved compared to trying to vary the dimensions of the capacitors. 

I agree the markings on the capacitors are a bit misleading. The 4.5 refers to the 9 capacitors that are in parallel and the 1 to the two capacitors that are in parallel to yield the (arbitrary example) 4.5:1 ratio.