It looks like you’re in pretty good shape if your decoupling is 0.8% 
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Regarding EF, it’s pretty meaningless to compare between riders - it’s entirely individual. It only looks at power and HR and not at any other characteristic of the rider. A big heavy rider will likely have a higher EF than a light small rider (would expect him to have a higher FTP) but might have a much lower w/kg.
It can be useful to track improvements over the course of a year. As regards improving it, pushing your FTP up over the course of a season will likely bring up your EF. What approach to take will depend on what you’ve been doing previously. Changing stimulus can be very effective.
If you’re looking at sweetspot there’s some great information to be found here or alternatively you could try threshold work.