Faux Time Line Cache without HD

I recently purchased a 4TB Seagate "Hybrid" hard drive witch includes an 8GB SSD on the controller card which is supposed to keep the most recent files loaded to the SSD portion for quick retrieval. I moved a copy of the Kelly Malone - Earth & Stars demo session to this new drive and monitored the disk activity when I first played the session and then again after I had played it 4-5 times. The differences are noticeable; The 1st time disk activity showed up to 7% max with an average of 4-5%, each subsequent playback saw it decrease a percent or two each time with the 5th time playing back it averaged 0-1% with a max of 2%. The pics below are the 1st & 5th time showing the disk activity substantially different at the same place in the song. I'm using Pro Tools 12 for this experiment. This may all be an accident or I may be on to something here (this is how my mind works when I have nothing to do). All always; YMMV!