It can only work for boosts. FP depend on many things. For exemple I produce 5 FP a day in a TF and miss a collection every other week (a cycle every 4 weeks) But some may use it to produce goods, or miss a collection once a week. Other exemple I collect my 8h FP production buildings twice a day, while some may collect them once or 3 times a day. Want more exemples? I hardly ever have unmotivated SoKs, but it may happen that you only collect coins. Or this one: what if my city has a weak defense and they always plunder a palace or two, sometimes a TF instead ect. My daily income will then be overestimated. A last exemple: what if my main FP income is from produce 2 saltpeter recurring quest? My daily income will then be underestimated. Boosts on the other hand are very stable.