Gigabit plan but getting < 200 Mbps to modem

Hello Xfinity experts,

I had Comcast xfinity internet installed at my house in late September (new underground coax cable installation). I purchased the Gigabit plan and a compatible docsis 3.1 gigabit modem (Arris SB8200). My wifi router is a Ubiquiti Amplifi dual-band mesh (model AFI-HD-US). Through the Amplifi app on my iPhone, I am able to run a speed test, which shows 161 Mbps down and 22 up. I have run this test several times over the past 2 months and the fastest I've ever gotten is 165 down and 37 up.

I realize the router can never deliver gigabit speed over wifi, but the router is connected via CAT6 ethernet cable to the modem, so I should be getting much faster than 165 down to the modem, right? The speed test on the xfinity website shows 189 down to the modem. I don't really expect 1000 Mbps, but I was hoping for 800. Am I dreaming, or could something be wrong?

Thanks in advance for your help!