High-precision (16 bit integer and 32 bit float) rendering is available in After Effects when the Project's Depth setting is either 16 bit or 32 bit:

A plug-in will be able to render in 16-bit integer or 32-bit float precision inside After Effects as long as it supports at least 16-bit half-float rendering internally.

If your plug-in is not capable of rendering at 16-bit half-float or 32-bit float, FxFactory will automatically convert your inputs/outputs to the only bit depth supported by your plug-in, 8-bit integer.