Capturing MIMO traffic and spatial streams

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Hello, I'm playing with frame capturing for my school project and one of my goals is to figure out if it is possible to capture all 802.11ac MIMO traffic and all spatial streams. I'm capturing in monitor mode with Alfa AWUS1900 (4 antennas) on specific channel (e.g. 36) and BW. I am able to capture frames that include radiotap headers and as I know there is a flag that indicates the number of spatial streams, filter for it is: radiotap.he.data_6.nsts. But when I use this filter it shows nothing, this flag is not availible.

So my question are: Is it possible to proove capturing of MIMO traffic and each spatial streams and how? How can I say that my captured traffic was send and recieved using MIMO?

Thank you for any advices.