Roland Pulfrew as
BrianTrousers correctly states - it is not a “bonus”, but a neat way to put consolidated pay up but giving more to those less well paid. For example, give £1k more than to those on £50k it is a 2% rise, but for those on £100k it is only 1%.
The only snag is you can’t do that too often as no one will want to get promoted as the pay jumps are reduced.