The following is related to a 80m OCF dipole 
(~135 feet total length)

* If you feed it at 8.9%, you don't lose any ham band (80m-6m)(no in
ham band sine nulls). Although the SWR will be higher on 80m.

* If you feed it at 16.6%, you lose 15m band (sine equals zero).

* If you feed it at 20% (20/80), you lose 17m and 6m bands (sine
equals zero).

* If you feed it at 25%, you lose 20m and 10m bands (sine equals
zero).

* If you feed it at 28.89%, you lose 12m band (sine equals zero).

* If you feed it at 30%, you don't lose any ham band (80m-6m).

Although the SWR will be a little higher on 12m.

* If you feed it at 33% (1/3:2/3) you lose 30m, 15m, and 6m bands
(sine equals zero).

* If you feed it at 36%, you don't lose any ham band (80m-6m).
Although the SWR will be a little higher on 30m.

* If you feed it at 41.6%, you don't lose any ham band (80m-6m).
Although the SWR will be a little higher on 17m and 12m.

* If you feed it at 50%, lose 40m, 20m, 15m, and 10m bands (sine
equals zero), but should do very well on 80m, 30m, 17m, 12m, and 6m bands.

This is a normal dipole, where you only get odd-harmonics.

By "lose," I mean the antenna will not be useable and will have very high
impedance (Sine goes to zero).

My first 80m OCF dipole was a 20/80 (w8ji) at ~40 feet. I used the Balun
Design 4115ocf balun (4:1). (No additional choke is needed with this
balun.) The balun is fed with 125 feet of LMR400 coax. My transceiver is
IC-746Pro (has built-in 3:1 tuner). I used the antenna for a contest, and
then I discovered it did not work on 17m & 6m, and did not work as well as
hoped on 80m (a ground elevation issue).
So I rebuilt the antenna for 36% offset, and presently use it 80m thru 6m
with IC-746Pro. I still may try to reconfigure it for the 30% offset
someday.
Hope that helps,
John - k8ba