I think I see where the additive comes into play...
But assuming as the birthrate is a constant and assuming L&P is another constant additive to birthrate
It should be able to be displayed as a ratio (BR "+" L&P)/BR which should translate to a clean %...

Yes I know that is pulled from the wiki... but the ONLY way I can think of where it "might" make a different change it to change some positions so that it reads

Peasants Hourly Change = (Current Peasants - Storms - Drafted Soldiers - Wizards Trained) * (Birth Rate + Love & Peace) * Homes Bonus * Chastity

I was thinking that the wiki equation was treating changes as what "would" happen in the next tick...
As opposed what last ticks effectes "were"...
But I am still seeing the same result again...

Only difference I see now us that BR is a "variable" constant of .0205 X (.95 through 1.05) and L&P "ADDS" and hard constant of .0085 to the "variable" constant.
Which (comparable to ToG's 40 - 80%) would introduce a range of % of improvment of about 39.5% - 43.7% increase (depending on the ± random 5%)