I am new to Trainer Road and am very early on into my first Sweet Spot build block. So far I’ve done the ramp test, Mount Field, Baxter, and Goddard. After the workout I analyze the ride and notice that while the workouts and intervals are targeting Sweet Spot, I’m not really in the Sweet Spot power zone for very much of the workout, even though I’m hitting the recommended power targets while riding. Typically I’ll be in a zone or two below - like endurance or Tempo - for a significantly higher percentage of the workout than Sweet Spot. Even when I zoom in on the Sweet Spot intervals themselves and single them out I’m still below the Sweet Spot power zone. My questions is this: Is this merely by design this early in the block as a way to build up fitness to prepare for other, more difficult Sweet Spot workouts? Or is it something else that I may be unaware of?
Do you have a smart trainer that has erg mode? If so, that is a good way to guarantee that you are hitting the correct power zone.
I do not, I am using a fluid trainer with crank arm power meter.
Week 1 with Mt Field and Baxter top out at about 85% of FTP, so slightly below what is classically thought of as “sweet spot” - and yes, this is likely to introduce people new to structured interval training to workouts at this intensity. But if you look ahead at week 2, you will see Goddard, Monitor and Antelope are all solidly sweet spot.
Just wait till the end of week 3. 3x20mins 
Enjoy the starters while you can… I’ve just failed my 3rd 20min block…that was after 20 minutes at 90% followed by 20 minutes at 94%… just couldn’t do the third 20 minutes at 92%… too much fatigue, but going to have a good go at Looking Glass tonight,(Tempo zone) 3x20-minute intervals between 75-90% FTP. The hardest one will be yesterdays easiest one!
The OP said they had done Goddard 
VVVVVVVVVV
The High Volume Sweet Spot Base plans are almost exclusively Sweet Spot power level work.
But Low and Mid Volume Sweet Spot Base plans consist of workouts focused at various power levels. In some cases, there may be only one Sweet Spot level workout in a week.
In this, the Sweet Spot Base title is a bit of a misnomer. But they use it in contrast to the “Traditional Base” name and plan design.
Don’r worry it gets harder! Mount Field is a tempo workout and Baxter is an endurance workout with very little tempo. Goddard is a bit of Vo2max mixed with two short low-end SS intervals. So you’re right it’s not sweet spot work. It will get there monitor then antelope this week. And it just gets harder from there. The first week is just to get your legs turning. The real work starts week 2. With a significant ramp-up week 4-5. Especially if you do the leg speed drills. Tunnabora will get to you. It looks easy but if you start at 90 RPM the 4th interval will be at 105 RPM. You’ll be at SS and low end treshold for the rest of the plan from now on.
Thanks for the info!