Lets start off with the field test. Yeah you need to find a good spot where you can do uninterrupted. Paths are probably not the best spot. Unless you an get out early before anyone is out there. But looking at the power it looks like you went out far too hard. Sometimes you should hold back in that first 3 - 4 minutes to let the effort come up to you.
Your first 3.5 minutes was at 340 watts which would have been 121% of your previous FTP. If you held that pace your FTP would hav been 323 watts. So quite a bit higher. So that is why we do talk about pacing out first 3 - 4 minutes as the effort will come up. Your power slipped through the rest of the 20 minutes. Sometimes with coached athletes we will give a 2 x 10 minute full gas workout the week before to help determine the pace. We can actually plan that next time for you! But with that said you do have to go off of feel with a field test, but again that is after the first 3 - 4 minutes.
It does look like you did a 347 watt effort in October last year but I don’t see anything close to that as of late. I do see you did a ramp test as well in the winter which would have yielded a 290 FTP which is close to where it is now. It seems accurate where it is now based on your efforts and weekend rides.
I would recommend one of the climbs you ride next time to do the test at. Find one that takes about 20 minutes and race from bottom to top. Can be a good way to do it.
You are doing a great job on your sweet spot weekend rides. You are getting between 45 - 60 minutes of sweet spot time. Also your TSS per hour has been 60 - 65 per hour range which is great! You are able to benefit from getting your sweet spot efforts in on climbs which is good! You can just go bottom to top at sweet spot and not think so much about the effort.
This past Saturdays ride you did start the climb pretty hard though and think you paid a bit for that hard effort at the start. Good to open things up a bit more though like a group ride, and maybe you were with others on this one.
Not feeling good yesterday makes sense as you just had done a 300 TSS day and are coming to the end of a training block! Fatigue is adding up. Actually your TSB (fatigue) is a the lowest point it has been in quite some time! So you have been doing more training and accruing more training stress than normal. But this is good and what we look for.
Also in the performance manager chart we can see your CTL (fitness) is increasing very well. Having a nice build up over the past block and can see with planned TSS coming up that the trend will continue. So just keep #FtFP’ing.
Next block will have some longer sweet spot and tempo efforts. After seeing your weekend rides you should have no problem doing the long sweet spot efforts as you already have been! You have been able to knock out some steady long sweet spot efforts the last 4 weeks.