A 27% return on investment can´t be correct, this is simply not sustainable. From where would such a high ROI be generated?
Let´s see where the mistake could be:

For $20 of units, dividing $0.063 by 20 gives a slightly higher daily accrual rate per dollar of $0.00315.

I take this number as a given (I was actually not aware about this).
I guess in this value it is not yet included the 50% share that goes to the curators?
For 20$ of units you have to pay at a rate of 33c/Hive (now it is slightly higher, but this is a good average of the last weeks) app. 60 Hive. So you invest 60 Hive and get a daily upvote reward of 0,00315 or rather 50% of that which is 0,001575.
Assuming you would post regularly throughout the year, those upvotes would sum up to 0,59 Hive. 0,59 is less than 10% of your investment of 60 Hive. If you would have powered up those 60, you would not only get the 2,8% Hive inflation but also the app. 8-9% of curation APR.

So I think it is better to keep your Hive with you. By this you have more control about them, and moreover you increase your stake and your governance value (witness votes, proposals).
Also you can engage better with others (and will be seen different) if your stake is higher, this could make a difference in the long run.