The IAP-224/225 was first supported on Instant 6.3.1.1-4.0.0. This version (like its ArubaOS 6.3.1.x counterpart) supports PoE efficiency mode on 802.3af power; but still runs 802.11ac at full capacity on 5GHz. You are probably not finding anything in the Release Notes for Instant, as it was never supported in 2x3:2 spatial stream mode.
This is an example of the output from an IAP-225 running on 802.3af power source. This was running 6.3.1.0-4.0.0.0; the first Instant OS to support IAP-224/225s.
IAP-225-DEMO#show ap debug system-status | begin “Power Status”
Power Status
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Operational State POE: One Ethernet port disabled; USB port disabled; 1x3 chain for 2.4GHz; 3x3 chain for 5GHz
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Current HW State POE: One Ethernet port disabled; USB port disabled; 1x3 chain for 2.4GHz; 3x3 chain for 5GHz
LLDP Negotiated POE Power 0.0W