Manual focus on old lenses

I just bought an M42 mount Takumar 200mm preset f3.5 lens, which is even better than expected.It's quite odd as it has 18 aperture blades. It's as sharp as any lens I own at f5.6, but when using focus confirmation I don't get results quite as sharp as I get in Live View. I was wondering if this is down to me or if there's anything about using lenses this old that affects focus confirmation, and if so, if there's anything I can do anout it. Or is it just wrong technique or something?

I find focus confirmation more often than not to be pretty accurate however at times once I have achieved focus I forget to refocus if either I or the subject move slightly but I am getting better at remembering

I find that by making slight adjustments on the focus ring slightly improves focus sometimes and trusting my eye rather than the little green hexagon you get a feel for it I think

https://www.pentaxuser.com/forum/topic/focusing-manual-lenses-on-k5--38428#comm430366