Reducing the corruption via PFM, since techs/skills affecting this don't seem to work?

[W4lt3r]

So yeah. After conquering entirety of Germanica and started on getting Gaul under my Roman banner, I noticed that my corruption levels are on 86.5%
Despite having 5 governors, each having political reformer maxed out, 3 governor generals with same trait and done with tier 1 and 2 philosophy tech trees.
This amount of corruption is cutting the tax income of my provinces to roughly 4000 a turn, while in trade I'm still banking about 16000.

Is there some modifier in the pack files to alter the rate of how fast corruption rises as your empire grows? I searched for a while through the forum and found a post by Dresden that this particular line would be in campaign_variables section, but found no such line there. Only lines I found were either related to effects of taking a city on some of the choices or then civil war modifiers.

Only line that I THINK might be related to this, would be the "settlement_looting_pct_region_gdp_reduction" but not quite sure. Can I get confirmation on this? *Edit* Nope, wasn't this one..

*Edit #2*
Found the tables for this. Dres2_campaign_variables. Two lines:
tax_efficiency_result_maximum_reduction (set to 130, reduced to 80%) and tax_efficiency_result_middle_reduction ( set to 50, dropped to 40)