Well, additive means the the two sources of flow are pushing in the same general direction so that their energies combine to move water in that direction. If one is pushing water to the right while the other is pushing water to the left, you just have a collision and the two flows tend cancel each other's energy out, so they subtract from each other. You want to create a flow like that in a river, where the majority of the flow is along the same direction.
In the case where you mounted the spraybar vertically, can you imagine what happens when the water impinges on the front glass? Some flow squirts out to the left and stalls against the left wall, some squirts out to the right, but it collides with the flow from the Koralia and stalls. Some flow squirts above or below and collides with the flow coming from the holes above and below. So in general the movement of water coming from the vertically oriented bar is incoherent, because water squirts out in every direction and weakens the total energy, especially if it conflicts with the movement coming from the Koralia.
A better idea is to aim for uniform flow, where all the energies are headed along the same path. If you mount the bar horizontally and point the holes level or very slightly down, you are creating flow distributed along a greater section of the tank. The water impinges on the front glass and most of the energy heads downward to the bottom. A little escapes off to the left and right but generally in the same direction from each hole. The downward flow the hits the gravel and has a greater tendency to be deflected to the back. Again, you do lose some to the left and right, but that's OK. If the flow is strong enough it then hits the back wall and rises up along the back wall.
It's by no means perfect and you need a strong flow rating from the filter but you can, for example mount the Koralia on the back wall pointing diagonally or pointing forward in the same direction. If your filter is strong enough you can add a second bar to give greater coverage along the tanks length and this will lower the velocity of the jets as they exit each hole.
You really have to play around with positioning of each pump/filter outlet, and don't forget that you should experiment with different placement of the diffuser, depending on aesthetics as well as effectiveness. If this is a 180L tank then the 10X rule says you need 1800LPH of flow "rating" ideally.
I've never had a bow front so I can't say how this affects the flow distribution. The bottom line with flow is that a majority of the plants should gently sway in the current. As biomass increases the flow becomes more critical.
Shouldn't the dosing be 40 ml 3X per week? You may want to double check that.
Cheers,