RollFast Fondo! So the important thing is going to be drafting! Going 4 hours and 25mph is not possible alone and you will need to stick with a group. Hang onto the front group as long as possible. Seems there are a couple of groups / riders that come in after the main group so just need to stick it out, find one and stay with it.
Last year it looks like you had a brutal start? What was the bridge with Tom? Did you stop? Get gapped off? That was a huge effort and something over the course of a 4 hour ride you want to avoid at the start. Norm power was 322 watts for 30 minutes which was close to your FTP, 98%! Not to mention a bit of an effort before that and you had the first 45 minutes at 311 watts and 95% of your FTP. That is a hard way to start and something that won’t be sustainable.
Position in the pack is important as well. Up front and you will get less of a draft. Typically there is a sweet spot in a group 10 - 20 back. Any further back and you can get messed up through a corner, gapped off, crosswinds and etc.
Sweet spot is the best training you can do really for this. It’s all about your aerobic engine and being able to stay on the gas for as long as possible. Important to find group rides to ride in as well to work on positioning, pack skills and speed.
The sweet spot work you are doing is perfect. You will want to continue that. You will want to mix in the 6 week road race plan as well, could even do the Fondo plan. Get that threshold work and some vo2 work in. Vo2 work is good for when you do hit the little hills and the pace ramps up. The sweet spot burst and crisscross workouts are great as well as the pace isn’t steady and you need to adapt to the changes in pace.
Had a great build last year and built CTL up nicely before the Fondo. You would need to do that again and time that out well. Probably build your peak CTL 6 weeks out with the Sweet Spot plans and then do the road race or fondo plan 6 weeks out to get that higher intensity in before the event.
Build up your endurance as well with long simulation rides. Ride 100 miles a couple of times the week building in with simulation rides. Ride a hard sweet spot ride for 3 hours, then 4, then 5. Keep that intensity factor of the ride up.
Over the winter you can do the fall foundation and resistance training program. Those will really help take you to the next level! Building some strength. This is good though the winter and also can keep you off the trainer a bit here in Indiana. Build the foundation.
Hydration and fueling is key along with losing weight so you are on the right track! Keep that up.