The "smart antenna" feature applies to AP-335 only.
It does not affect antenna patterns, and does not change the fact that the 335 is optimized for horizontal (ceiling) mount.
It simply enables a feature on the AP-335 where the software will dynamically select between a vertically and horizontally polarized antenna element for each of the four radio chains of the 5GHz radio.
The antenna patterns for these elements are roughly the same, but by selecting the optimum combination, we can improve the signal quality (SNR) in both transmit and receive direction, which may result in a higher sustained datarate (MCS) for a given link.
That's all.