You read my blog navagrahastro.blogspot.in and you will understand all the planets act in tandem and not the way you think. During a particular mahadasa, that planet does not come close to the native and influence more. Sun gives the same rays to everyone and is at the same distance from the earth everyday at a given longitude and latitude. So the Dasa system is not the ultimate in timing the events. The strength of the houses is what matters and vary from person to person.