Description
Harbingers Black Blade of Disaster summon remains at +32 attack bonus, though I have Improved Weapon Hex feat and I also have Caster Level 28 (through 26 Harbinger, 4 Warlock + Eldritch Patronage feat). This should put it 2 steps above the starting +32 attack bonus (though how much it increases with each step, the wiki or feat description doesn't say).
Expected Result
A Black Blade of Disaster that has been increased in attack bonus 2 times for an unspecified amount
Actual Result
A Black Blade of Disaster with +32 attack bonus, which seems to be the baseline from the wiki summons
Steps to reproduce
Take 4 warlock, 26 harbinger (with Dark Focus: Dark Seraph)
Take Eldritch Patronage (to count as 2 levels higher when using class feats and spell-like abilites)
Take Improved Weapon Hex
Use the class feat to summon a Black Blade of Disaster
Screenshots
Notes
The caster level bonus from Eldritch Patronage seems to work as intended in general, trying the crimson count(es) variant, summon humonculos was at tier 3 (triggers at CL27), Mortality Undone gives Epic Toughness 2 and such (triggers at CL28), so that part seems to work.
Tested on windows 10 in the Underdark on the mighty Zan-Yfranoth, that you can invisibly hammer him with Black Blade of Disaster as he stands around has been burned into my memory on a wizards from years ago, very important note it was.