The tech that purportedly increases army camp production by 15% only increased it by roughly 4% (95k to 99k). Anyone else having this issue?

It is additive to your advancements and artifacts. If you have +100% army camp gain from advancements, your result from tech will be lower in %

Right, the 15% is applied to the base value, prior to any of your passive advancements, boosts for watching ads, or anything else

Yes, this games calculates differently than nearly all idle games I know.

Armies=armybaserate * (modifier1+modifier2+modifier3+...)

Others I know do
ly all idle games I know.

Armies=armybaserate * modifier1 * modifier2 * modifier3

(multiplication results in a more constant speed throughout the game, while the addition results in a slowdown, even if you have many modifiers)

It seems to be a deliberate design choice.

It's definitely deliberate. In the end, it doesn't matter, making it multiplicative instead of an additive bonus would just result in the bonus drop from 15% to 10% (or whatever) appropriately to achieve the same result.

But it would certainly be easier for players to follow the math if was straight multiplication. There are lots of confused players talking about this because a 15% upgrade only provides a 4% benefit (etc).

Interestingly, the bonus from watching ads is multiplicative, so the formula is:

base * (100%+15%*(number of army camp techs)+xx%(from advancement)+yy%(from artifacts) ) * 120% (from ads)

Bonus? Ads? Nothing for PC web browser players =/ meh

I think this all could be stated clearer somewhere and the effective boost isn't obvious sometimes, but I think for this game it's fine that way. What might be to our advantage, though, that decreases should work the same (I can't back this with numbers unfortunately): So if you have two increases of 50% each, the multiplicative approach gives you 2.25 times the income, while the additive approach only gives you 2 times the base. For decrease, two factors with 30% each gives you 0.49 % of the base the multiplicative way, additive they give you 0.4 times the base. So e.g. upgrade costs should get lower than they would in other games that used the multiplicative approach.

From my observation decreasing bonuses work the same. Well almost always the same. For example when I recalculate recipe times, or resources needed in recipes in my WZI spreadsheet it works the same and the decrease values are calculated from base values. However I've been having issues with mine upgrade costs. The bonus values there obviously are not calculated from the base values as they are significantly lower than they should be if it was so.