No. I have tested it a lot. It's not true in case of Chanter's amulet and Boots of Leader for paladin. This two items increasing base value by 10% and then this value affected by int. (BASE*1.1) + Int modifier in persent. That's how this work.
Test it yourself if you don't believe me.
Then why is the inner circle of the chanter's AoE indicator (=base radius) not changing while the outer cirlce widens by 20%?
It says 20% in the description, too (not that this is proof or something).
I just tested it 30 seconds ago to be sure. The inner circle doesn't move. How did you test it? By adding/substracting INT while wearing it? Maybe the indicator doesn't adapt to a change of base radius.
I'm testing it right now and don't understand.
Ring of Overseer (+10% to AoE) with chanter having 20 INT (+60% to AoE):
Chanter with 20 int have 4*1.6 = 6.4 radius. Ok. Then i equiped Ring and radius of Beloved Spirits became 6.71 meters. I have no idea how this value appear!
(4*1.1) * 1.6 = 7.04. Wrong.
(4*1.6) + 10% = 7.04. Wrong.
(4*1.7) = 6.8. Wrong.
I guess VotMt only gets calculated as base when it comes to INT, not when the increase of Overseeing is calculated?