Russia Ukraine war, page-170920

I believe you are correct

https://www.telegraph.co.uk/world-news/2023/08/26/ukraine-offensive-russia-defences/

The current line where the fighting happens is the most fortified and most mined. The other lines are much weaker and are designed to be strengthened in case of first line failing but also provide protection from occasional small breaches and to allow safer troops rotation and supply.

I havent seen any reports saying the next lines are much more fortified the the one being attacked now. But happy to be corrected