I’ve bought points once or twice before. Enough points for 2 business class tickets back from UK ( via Mauritiushum I wonder if the percent bonus is random or based on your customer profile. Can those who received > 100% share their profile; e.g. do you fly AC paid fares a lot, are you more than a basic member, have you bought lots of points in the past???
for myself on the base bonus of 100% - I have bought points in the past during promos - say 250,000 in total - earned minimal points on paid fares - am an entry level member - do not have any CCs which accrue points which can be transferrer to AC.

Never flown Air Canada.
Maybe I was just lucky.