Listener envelopment is typically investigated in listening experiments with stationary or quasi-stationary sound fields, generated by multichannel noise signals or diffuse reverberation. In this contribution, we propose experiments using non-stationary sound fields to extend a recent model established using stationary multichannel noise. This requires a synthesis approach to generate sound fields with adjustable fluctuation across time and direction as dimensions. While temporal and directional sparsity can evoke the perception of localized auditory objects, a temporal and directional density above a certain threshold supports the perception of envelopment. The presented listening experiment aims at investigating this threshold, and the spatial auditory perception above and below. Based on the results, perceived envelopment can be modeled for sound fields of fluctuating anisotropy.