I have been cleaning sewers in the the Chicago area for 24 years now. Most homes here have 4" cast Iron under the house and when it leaves the house approx 5' out it goes into 6" clay pipe. These homes only have a 4" clean out on the stack so trying to get a 6" expanding cutter through the line is real pain in the arse. So I have learned how to clean the line properly with a 4" cutter. We start off with a 2" then to a 3' and finally two passes with the 4" cutter cleans the line out extremely well. I had a village inspector put a camera in the line to try and prove to me that I "needed" to get the expanding cutter through. To his surprise the line was root free. Our company guarantees its power roddings of the main sewer for two years.
Now to address the roots growing in the top of the pipe here is picture showing such. And Rootx will get to the roots growing in the top since it does foam through the whole pipe. Now I have seen clay sewers that are over 100 feet long trees growing around the area like a forest preserve and not a single root growing in to the drain at all. The old timers used to know how to properly install the clay pipes. The issue with the pipes installed from the late 1960's to present day is all this labor saving crap like slip-seal joints.
Some people say PVC sewer lines will never get tree roots, they lie. A fact roots grow in through the joints in the sewer pipes. Yes clay comes in 2, 4 and 6 foot long pieces. Most common is the 2 footers. So every two feet roots can grow in the pipe. Plastic SDR 26 sewer pipe comes in 13 foot lengths which roots will still grow into but much less joints for this to happen. Here is a picture of roots pulled out of a plastic sewer line.
If RootX does not help we recommend to all our customer's that do not want to dig and replace the sewer to have the sewer properly rodded every two years as preventive maintenance. Just like you have to cut your lawn every two weeks. Oh another thing that can help is water your trees, get root feeders and and that and keep your trees watered. This will help the grow in the soil instead of seeking out water in the sewer pipes.