Comcast throttling ipv6 throughput?

[kriteknetworks]

A couple months ago I noticed my throughput on HE tunnel was considerably lower than ipv4 throughput.
Speed tests over ipv6 using Comcasts speed test to IL server consistently show 9-12Mbit down, 10-15Mbit up.
Other ipv6 speed tests show similar behaviour.

I haven't altered any default tunnel settings, they have worked for years.

When disabling HE tunnel and using Comcasts ipv6, I get same rates as ipv4, ~125Mbit down, 25Mbit up.

I tried engaging two ipv6 evangelists at Comcast, John Brzozowski and Jason Livingood to find out why I
was getting this behaviour, but because I could not get an HE tech to get involved, they dropped the discussion.

Has anyone else using Comcast noticed this behaviour?

[cholzhauer]

I can see there being a little bit of overhead, but nothing that would cut your speeds by 10x

Interested to hear how this turns out.