I just changed my 30" RWO extension to a 36" Harken (omniflex?)

I agree that the geometry thing is a challenge when mounting. My suggestion is to elevate the stern of the boat so that you can lower the rudders. The tiller cross bar will be the normal sailing position.

If you are using an RWO extension, they only swing through 180 degrees. I have found that I want the extension to swing lower than horizontal. To to that, it must be mounted slightly forward of top dead centre position. Try taping it in place with electricians tape to see if it is what you want. When changing tacks, the extension simply flops to the back until you are on the new tack.

The Harken extension will go past 180 degrees so it may be possible to mount it top dead centre. I haven't used mine yet although I still plan on mounting it slightly forward.

I'll report back later today if it doesn't rain.

Don