When trying to understand off center fed antennas, it's important to
realize a few key facts:

1. A properly working "voltage" or "Ruthroff" balun will force common
mode current to exist on the feedline in its attempt to cause equal
voltages on the unequal length sides relative to the feedline shield.
2. Even if an effective "current" or "Guanella" balun is used, feedline
current will still be induced by the uneven coupling between the two
antenna sides.
3. A transforming balun is very unlikely to effect the expected
transformation ratio, and is likely to add a significant amount of
series and/or shunt reactance except at those spot frequencies where the
match is close to perfect.

This isn't to say that off center fed antennas can't sometimes be made
to "work", i.e., provide a reasonable impedance match on some bands. But
when they do, it's not for the reasons you think from an analysis
assuming a perfect transformer and balun. It usually involves a complex
relationship among the particular imperfections of the
balun/transformer, feedline, and path to the Earth taken by the feedline
shield.

Roy Lewallen, W7EL