antennae placement

I have seen some theremins have plate antenna ,and was wanting to know why the part the plate was on in this case it was wood did not efect the pich or the volume

I don't think the wood would have much of an effect on the pitch or volume. Even if it did, it is a fixed object so the effect would be predictable.

For instance, I put a Barbie doll head on my pitch antenna after poking myself in the eye at a gig. She affects the pitch a little but not enough to bother me and the affect if constane so I just tune the instrument to compensate.

I would guess that the player's hands might affect either one, though.

I like having the antennae separated a bit.