That isn't true Dave, Twin Truckers are fed in phase. There isn't any
front to back ratio. When mounted 1/4 wave apart on a vehicle,
perpendicular to the axis of the vehicle, the pattern is more oval
shaped inline with the vehicle.

That's what I was referring to, but I was in a rush, and wasn't clear.
The intended app is to concentrate power along the (presumably straight)
road, in front, and in back of you. As you depart from 1/4 wave spacing,
that deteriorates.

If you decrease the spacing the
pattern becomes more circular or less directional. There is nothing
wrong with that, but you could obtain the same pattern with a single
antenna. But it wouldn't look as nice as 2 antennas swaying back and
forth.

It gets pretty spiky as well, which sucks.