The problem with 0.7 BR matchmaker is that it only partially decompresses things, and not completely.
It would easily change it so that vehicles don’t have to face much tougher / weaker opponents, but doesn’t balance out vehicles that are too weak in one BR, but too strong in another BR.
For example, the KV-1E/B may be too strong for 4.0 (despite the 0.7 BR matchmaker) mainly because most 4.0s still struggle with it.
If it were to go to 4.3 in this 0.7 matchmaker, it would be too weak, as most 4.3s may be able to kill it, as well as the fact that now it faces 5.0s like the VK3002 and KV85.
Let’s take the XM803, MBT-70, and KPZ-70 as another example.
XM803 is 9.0 at the moment, whereas MBT-70 and KPZ-70 are 9.3.
XM803 is worse than the MBT-70 (worse HP/TON, and no 20mm), whereas the MBT-70 is worse than the KPZ-70 (less smoke grenades, worse HP/TON, 7.5s reload instead of 6.0s).
If the Matchmaker was decompressed to a 0.7 BR max range, vehicles that get exceptionally outdone (the 8.0s for the XM803’s case, and 8.3s for the MBT-70 / KPZ-70’s case) would no longer have to face them.
Equally, the XM803 / MBT / KPZ would no longer have to face 10.0s and 10.3s respectively.
That is pretty good if we want players to feel like it’s more fair.
However, the BRs themselves will have issues of inbalance, where one vehicle is too good for one BR, or too bad for the other BR.
The MBT-70 is objectively better than the XM803, but is objectively worse than the KPZ-70.
So you could either move the XM803 to 8.7, and the MBT-70 to 9.0 (which may or may not be fair for the 8.0s that now have to face the XM803).
Or you could move the KPZ-70 to 9.7 (which may or may not be fair for the KPZ-70 as it now has to face 10.3s).
The optimal solution to this is increase the max BR range such that the MBT-70 doesn’t lower its inferior version down in BR, but also doesn’t needlessly increase the superior version up in BR in the other alternative.
Let’s say all 9.7+ vehicles get moved up by 0.3 BRs.
The KPZ-70 would then be moved to 9.7 and would still face the same enemies in a full uptier as it was before. (The 10.3s would then be 10.7).
The MBT-70 would then stay at 9.3, and so it would no longer be at the same BR as the superior KPZ-70. This would allow it to no longer face 10.3s (that are now 10.7).
The XM803 would then stay at 9.0, and still be a lower BR than the MBT-70, and no longer has to face current 10.0s.
The problem with this is that 0.3 is not enough to decompress everything, so it may require a max BR range of 15.0 or something before everything is fairly balanced.
In the situation above, it would make it such that the KPZ-70 may not even have to face 10.3s, and the 8.0s / 8.3s may not have to face the XM803 / MBT-70.