Necromantle MAY not be working as intended

The base respawn rate for minions is 8 seconds, with this equipped it is reduced to 5 seconds not 4 as it should be. Further, if you have every reduction in the game Passives, Items etc the lowest it will go is 3.5 seconds. The math does not add up. 8 seconds = 100% of time. If we assume that they are not additive and instead cumulative then the total reduction should be 8 Seconds reduced 50% to 4 seconds. 4 seconds reduced 25 % to 3 seconds. 3 Seconds reduced 15% to 2.55. 2.55 reduced 5% to 2.42 and finally another 5% to get the final number of 2.30. Is it just that the game displays any decimal over 2 as a 3? Or is it actually making things take 1 second longer than they should. Would love if someone else with minions could test this to see if they get similar results.

My conclusion was that Necromantle is adding an additional 1 second into the mix by not reducing the numbers as intended.