After making clear how tax base works, I have renewed my study. As a sidenote, tax base includes your capital bonus, temples and half of your vassal's tax base.
The examples are no longer restricted to OPMs.
Observing from the Ottomans, after annexing Albania. Tax base=100.
Country name; tax base; opinion modifier
Connacht; 4; +30
Naxos; 5; +30
Munster; 6; +30
Mecklenburg; 7; +29
Urbino; 8; +2
Liege; 9; -17
Aachen; 10; -31
Magdeburg; 11; -41
Salzburg; 12; -49
Serbia; 13; -55
Brunswick; 14; -59
Yemen; 15; -63
Oman; 16; -67
Pomerania; 17; -69
My conclusion: if target state has a tax base smaller than 7% of yours, then a +30 opinion bonus will apply. If target state has a tax base larger than 12% of yours, then you need to have huge positive buffs to offset the 50+ opinion penalty. If the tax base ratio is between 7% and 12%, then the vassalization will be somewhat similar to 1-3 province states pre-1.2.
The examples are no longer restricted to OPMs.
Observing from the Ottomans, after annexing Albania. Tax base=100.
Country name; tax base; opinion modifier
Connacht; 4; +30
Naxos; 5; +30
Munster; 6; +30
Mecklenburg; 7; +29
Urbino; 8; +2
Liege; 9; -17
Aachen; 10; -31
Magdeburg; 11; -41
Salzburg; 12; -49
Serbia; 13; -55
Brunswick; 14; -59
Yemen; 15; -63
Oman; 16; -67
Pomerania; 17; -69
My conclusion: if target state has a tax base smaller than 7% of yours, then a +30 opinion bonus will apply. If target state has a tax base larger than 12% of yours, then you need to have huge positive buffs to offset the 50+ opinion penalty. If the tax base ratio is between 7% and 12%, then the vassalization will be somewhat similar to 1-3 province states pre-1.2.