I recently saw a question on a forum that I put in the description. I only answered in general terms at the time, as I didn't want to bother with a detailed description, but the question didn't leave me alone, so here it is :

In fact, this is essentially an eighth grade physics problem as it is quite simple.

I suggest to do some interesting maths.

First, we must decide what we are looking for in the first place. So the basic formula for calculations is :

We will also attach a graph on which we will mark some points and parameters of interest.

As we can see from the equation above, we need the horizontal and vertical velocity of the projectile for the calculations. This is the simpler part of our formulas and should not be difficult to calculate.

Next we recall the equation of motion with acceleration, and write down its vertical form, we will need this in order to calculate the time for the projectile to rise to its maximum height and fall to the height of the target.

We recall the solutions to quadratic equations and solve our equation relative to time, obtaining approximately the following formula :

very important note that we have the trajectory of the projectile crosses the height of the target twice because it is parabolic, but we need only one point, so the formula will have the following form :
It can be this

or this

but we need only this point

so ...

Then the horizontal distance to the point of incidence will be expressed as :

We can now implement this in SP through the variable editor :
Muzzle_Velocity = speed of projectile (m/s)
elevation = gun elevation(degree)
target_height = target height
self_height = Initial height. (This measurement must pass through the axis of rotation of the gun as this has a strong effect on accuracy).
g = 9.8066
v_x = cos(elevation)*Muzzle_Velocity
v_y = sin(elevation)*Muzzle_Velocity
impact_time = (v_y + sqrt(v_y*v_y - 2*g*(self_height-target_height)))/g
impact_distance = impact_time*v_x

Note

The projectiles in the SP are not affected by air resistance, which makes it possible to use such a simple formula.