I think 6weeks should be plenty enough to tell if youre improving in sessions. If youre not improving in sessions, youre not going to be improving in races. Easy running will adapt your body over many years but digging a hole with sessions that arent working and hoping that one day itll just turn around is just magic thinking.
Another FT type here. My 2cents, just forget threshold running altogether, except maybe the odd mara paced steady run for conditioning. We do better off shorter efforts with more changes in pace. 200s and 400s are grand, with some 800s and 1ks to prepare for racing. Probably benefit more from variety as well, hills, drills and weights.