SQM not limiting Steam downloads? plus other questions

I have been using Gargoyle for years and decided to try something new. What kept me using Gargoyle is the Active Congestion Control QoS feature that automatically keeps ping times at a user defined setting on my wireless connection, where the download bandwidth changes wildly with the weather. But I read that SQM has a "autorate-ingress" feature that aims to achieve the same thing.

Today I sysupgraded to OpenWrt on my Linksys WRT1900ACS and have been learning about and testing the SQM feature according to the man page.

My current settings are

root@OpenWrt:~# cat /etc/config/sqm

config queue
        option debug_logging '0'
        option verbosity '5'
        option squash_ingress '1'
        option ingress_ecn 'ECN'
        option egress_ecn 'NOECN'
        option interface 'eth1.2'
        option upload '4000'
        option qdisc 'cake'
        option qdisc_advanced '1'
        option qdisc_really_really_advanced '1'
        option enabled '1'
        option linklayer 'ethernet'
        option download '70000'
        option overhead '44'
        option script 'piece_of_cake.qos'
        option squash_dscp '1'
        option iqdisc_opts 'autorate-ingress rtt 40ms'

When I have Windows pinging, I get good ping about 30-40ms. Then I constantly run ookla speedtests and SQM keeps ping the same range. But when I start a download in steam, pings go upto 100-200ms. What can I do to stop steam increasing ping times as much? The ookla speedtest download result is always ~50% lower than steam so it is like steam is bypassing SQM? When I turn off autorate-ingress steam doesn't cause pings to increase but don't get the benefits of dynamic bandwidth estimation on wireless links.

Also I don't really understand what the option "rtt 40ms" does. I can see in the output below that "interval" is now 40ms but what does interval mean? When I set rtt to 200ms, nothing seems to change regarding Windows ping times.

root@OpenWrt:~# tc -s qdisc show dev ifb4eth1.2
qdisc cake 812b: root refcnt 2 bandwidth 29432Kbit autorate-ingress besteffort triple-isolate nonat wash no-ack-filter split-gso rtt 40.0ms noatm overhead 44
 Sent 361346 bytes 3795 pkt (dropped 0, overlimits 3553 requeues 0)
 backlog 0b 0p requeues 0
 memory used: 7296b of 4Mb
 capacity estimate: 31395Kbit
 min/max network layer size:           46 /    1352
 min/max overhead-adjusted size:       90 /    1396
 average network hdr offset:           14

                  Tin 0
  thresh      29432Kbit
  target          2.0ms
  interval       40.0ms
  pk_delay        314us
  av_delay         45us
  sp_delay          3us
  backlog            0b
  pkts             3795
  bytes          361346
  way_inds            0
  way_miss           17
  way_cols            0
  drops               0
  marks               0
  ack_drop            0
  sp_flows            6
  bk_flows            1
  un_flows            0
  max_len          1366
  quantum           898