Just expanding on something i talked about earlier, i think Sight Towers for probes are rather overused to just scout the entire map for incoming Thor's that just adds to the ever increasing frustration for even four Thor's and especially for when it becomes three again. It becomes literally impossible to sneak up on a probe and when they go on high ground as soon as you go around to get them they just blink away which results in constant scans and multiple Thor's to pin down a single probe.
I understand there is a practical purpose for them though for blinking to higher grounds and such without going noticed, my suggestion would be to increase the sight towers cost enough to make them not just be some cheap luxury item that can be thrown around the map for comfort and peace of mind but rather something that can be afforded once a player has an fairly established base. It also adds to the excitement of the game knowing that a Thor could be blasting his way to your base at any moment and you never know where they might strike. To help with the other practical purpose they served perhaps create another ability/structure for probes that temporarily grants sight of a nearby area, say a missile turret which grants sight that instant builds and then self destructs 5-10 seconds after it was built. Then place a cool down on the ability/structure depending on how much it effects the game play and so it cannot be just spammed to achieve the same results as a sight tower. It would have a much smaller radius of sight similar to the sight tower as its being built maybe even smaller so it can't be abused.
Feel free to share thoughts and ideas on this.