chasing the yeild curve, page-15

The dividend yield on WBC has dropped from 8% to 5.8% due to the increase in sp from $20 to $28. Interestingly an increase in sp of 40% has only reduced dividend yield by 2.2%.

I don't quite agree with your conclusion, as you are not comparing the right figures.

If WBC at $20 had a dividend yield of 8%, then that means the dividend is $1.60. The same dividend when WBC is $28 gives a dividend yield of 5.714%

The share price has increased by 40%, but the dividend yield has decreased by 28.75%. From 8% to 5.714% is a 28.57% drop (forget that your are comparing the change in values of percentages, just think of it as going from 8 to 5.714 means a drop of 28.57%).

This is what you would expect mathematically.

Something going from 100 to 140 is a 40% increase. Something going from 140 to 100 is a 28.57% decrease.