Using two WAN if's with MWAN3 - improve load balancing

I am using 19.07 on TP-LINK TL-MR3220 v2 (don't judge me) with one broadband pppoe WAN (~ 70 Mbps, ~3 ms ping) and a smartphone-tethered unlimited 4G WAN (~30 Mbps, ~70 ms ping) as a fallback via MWAN3. Its current default "balanced" policy config implies all connections go through both interfaces in the configured weight proportion regardless their current bandwidth usage (i.e. with 60/40 config 6 of 10 connections go through the primary interface, and 4 of 10 go through the fallback one). The problem is a random service may need a fast connection but may be "unlucky" to be assigned to the slower mobile WAN interface - this is totally unpredictable, so I had to switch to "wan1_wan2" policy. With "wan1_wan2" policy I have connections going through wan2 only if wan1 is down, so wan2 is idling 99% of time.

The question is: is there any way to configure it so wan1 being used as the only interface unless its bandwidth reaches some predetermined bw threshold (i.e. 70 Mbps) and keeps being so for the next, say, 20 seconds so the upcoming connections go through wan2? This would be a 1 1/2 bandwidth increase (in my case) with multi-connection services (i.e. torrents, multi-client downloads, simultaneous internet usage of different services by different LAN members etc).

You could use a more accurate ratio of 70/30 in balanced
Plus you can make more policies for specific connections to use the m1_m2 primarily, or make another custom balanced policy with a different ratio.
mwan3 doesn't count the bandwidth, however if you do such an implementation maybe you could run a script to change the policies used. But I don't know how would mwan3 handle the restart/reload of its configuration with active flows.

This was the first thing I had done upon the initial MWAN3 configuration (it is 80/20 actually), but it still doesn't bring the desired result within my setup.

I thought of measuring the current bandwidth with tools external to MWAN3 (like vnstat etc), but if I get MWAN3 reloaded via a script trigger, I am rather sure the active connections would get reset (WAN connections included) and the overall speed would drastically fall. I haven't tried this yet, as my device is 4/16 and my custom owrt build lacks even opkg to get any monitoring tools installed.

It seems that any further testing will have to wait for a while then.
In the meantime maybe @feckert or @aaronjg could provide some information from their side if that is something that could be implemented.