Garmin Training Effect

Been recording on my Fenix 6 to also get a Training Status on Garmin Connect. I did Carson (60 minute, sweet spot) but only got a TE of 2.6 (maintaining aerobic capacity). How much work is needed to Improve Aerobic Capacity (ie 3.0 +). Realise these are different tools, and the accuracy of Garmin TE can be challenged, but I would have thought an hour long sweet spot would be expected to improve capacity, not just maintain.