Does the effects of poison stack in Kingdom Rush?

In Kingdom Rush, one of the upgrades for for the lvl 4 Archer's Tower is poison, which deals 15, 30, or 45 damage over 3 seconds depending on how upgraded it is. Let's assume that I have 2 maxed out Archer's Towers right next to each other.

If both towers hit a minion at the same time, which of the following happen?

1. The minion takes 90 damage over 3 seconds. (Double damage)
2. The minion takes 90 damage over 6 seconds. (One effect after the other)
3. The minion takes 45 damage over 3 seconds. (No stacking)

Solution 1:

According to Rangers Hideout - KR Wiki the poison damage does not stack.

Poisons enemies, causing them to take True Damage over 3 seconds. A Rangers Hideout upgraded with Poison Arrows prioritizes enemies which are not immune to poison but are not currently poisoned. This effect does not stack.

But it still might be a useful strategy since each tower tries to fire on enemies that are not poisoned. The only problem I see with that is that both towers fire on the same unpoisoned enemies, which would decrease your overall DPS.