Hello,
This is an area that interests me as well. I've been looking at chip antenna radiation patterns, which are also indicative of sensitivity. In particular, I'm interested in transmit/receive performance within a 3D space.
TI has some information on antenna performance that you may find useful in extrapolating the effects of orientation.
See: http://www.ti.com/lit/an/snoa519a/snoa519a.pdf for an example.
Another [non-TI] example can be found at www.pulseelectronics.com/download/2964/w3008_w3008cpdf
Best wishes to you.