Disagree.
Factories don't have a on/off effect like towns have. Towns can only be captured once a specific threshold is reached. Factories (and the city). Have a gradually effect form the very start, from the first to the last building destroyed, they do not have any threshold. That is the main difference between those two target types.And it's not even measured in percent, but in minutes.
Your proposal just makes it easier to get the maximum downtime effect of 150 minutes, but I do not see any need for that. 20% strat status gives 126 minutes object downtime already, that is pretty much. I do not see any need to increase that.