But if you feed a coaxial collinear at the center instead of at an end,
the top and bottom portions will have tilts in opposite directions, and
the maximum of the pattern will remain perpendicular to the axis of the
antenna, at least over a broad range of frequencies. The gain will
change, but not drastically; matching properly to the feedpoint over
the range of frequencies is likely going to be the bigger issue.

And if the OP puts the gain antenna on a panel which can be tilted at
various angles, the performance may well be far from what he really
wants. I'd suggest a small stand of some sort that will keep the
antenna in a fixed position, if the panel can move.

Cheers,
Tom