I've tried to do some counter artillery in tier 5 and 6 games and found some success against leFH18B2's and M44's in my Grille and Hummel grind. What I do is basically this:
Let's take Paris as an Example, you'll see in the image link that the usual positions of both enemy and allied Artillery are marked on the map with boxes with the lines of fire indicated by a small line. If you wanna play counter arty, be ready for retaliation by always changing positions while waiting on your reload(you'll notice M44s don't do much of that because their reload is pretty fast, so they tend to get lost in the sauce).
Next up is actually counter firing on enemy arty, which is pretty straight forward. All you have to do is look into the usuall positions at early game and if you see the enemy artillery's shot trail leading from where his vehicle is firing, you just carefully aim in on it and fire. If you don't see much movement after a bit of a stake out all you gotta do is look where your Heavies are getting hit from, in this next image you'll see that the enemy arty are marked as red boxes and your heavies are in the usual choke point where they duke it out with enemy heavies, what you do here is take advantage of your eagle-eye view of the game by zooming out to get a general idea of where from your heavies are getting hit, from there you can just draw a visual line directly to the other artillery's position as shown.
I've noticed that most of my success happened from one-shots, because the moment I barely graze or miss an M44 or leFH18B2 they just relocate after firing afterwards.