to be that close (for longer durations) to your 6 week best effort is really pretty good. knowing that you’re only riding 2.5 hours a week, that isn’t too surprising but there are many factors which will keep you 5-15% off your “best ever” for any interval. many routes simply don’t have the conditions to absolutely crank for 5 minutes, or a 20 minute stretch will have lots of stoplights, or wet roads, or whatever.

it’s really unlikely that you need to eat (or even drink) a bunch before a 45 minute ride. just something small to get your body going, stretch, jump around a bit, wake up, go.

as to the significant difference at the burst end … did you actually TRY to do a best effort sprint for 15 or 30 seconds? i know that for me to push that curve up, i have to try and do so. i’ll identify a slight downhill or uphill or sufficient length, get the heart rate close to max (which for me is 115-120) and the speed to the right zone for a high gear peak cadence effort before that section starts, look at my timer, and then stand up and crank it as hard as i absolutely can. a quick glance down once or twice tells me where i am relative to the part of the curve i’m trying to push up (30 seconds, let’s say.)

i don’t know if this is true for everyone, but my heart rate and especially blood pressure are notably lower in the morning, which results in overall slightly less output for the same degree of perceived fatigue.