High Volume vs Mid Volume

I’ve been using trainerroad for four seasons now. I’m completed multiple full seasons using the mid volume plans. This year I had a bit more time on my hands so I decided to try the high volume plans for base. I couldn’t keep up with high volume for build so I went mid volume. Now I’m back to having more time so I’m going back to base. With that being said here is the question/s that I have:

If I end up dropping the hours to something in between mid volume and high volume, where does the sweet spot only approach not make as much sense vs the high intensity mid volume approach? High volume is on average about 9 hours a week and mid volume seems to be about 6 hours a week. What is a good weekly TSS to gauge at what intensity you need your day to day training to be?

Would it be better to go with the mid volume plan and then add workouts on top of that when I want or to subtract workouts from the high volume plan? That is really the gist of what I’m asking.

Thanks for the help.

probably, and not sure in this environment why you’d want to add the fifth day of intensity over adding z2 if you have the time.