I don't recommend the mortar mode on anything except the Tempest Launcher. Plasma Cannons, especially, received that MASSIVE nerf that lowered the projectile speed of the blast to slower than Sprint speed, making it disappear at ~75m or so if it doesn't hit the target. You should probably focus on only using the direct fire and keeping yourself high. The PC is in a horrible place right now, and I think focusing on what makes it good instead of intentionally gimping yourself may be the best option.
Plasma Cannon mortar mode has been fixed to be viable now. ToC/VI used it against DLB/FBI on Fort Ronan to great efficiency.
Biggest mortar tip? Don't fire it blind through windows (as officially promoted), unless you want to be kicked. Also solo play as far away as possible from other team mates to save them running in front of you right at the less second to also avoid "bad behaviour kicks".
The map doesn't predict the future positions of players. You could have no friendlies showing but by the time the mortar shot reaches its destination, half you team could be standing underneath it and that's not even firing it blind. The only real safe way to avoid TK's with it is not use it at all. AoE is most effective against groups, unfortunately that is where 99% of the action is going on at the time so eggs are going to be broke if you want to use it effectively. This is my biggest issue with EC. It punishes people who use weapons as intended. Don't even get me started on rockets.. The sin system is lazy and completely thoughtless.
Well when I say check the map, it's play with it, not just look at it, say "checked", and happen to unload all the magazine inside the building. On fortress map, I use it to breach on fortified heavy troops (work like a charm), and generally everyone wait for me to breach since they can't go through anyway. I rarely TK someone using the tempest, I generally kill myself a lot, bringing with me the melee dude who tried to kill me. Mortar is a underestimated weapon which ask for a lot of map read.
I will put forth a scenario where the mortar mode is fairly useful, and that's bombarding foes at a lower elevation. Thanks to the arch you can crouch down into a position where foes a way away cannot hit you and you can still hit them, provided they are where the plasma ball is by the time it gets there. That being said, if I were to suggest a quick fix to these weapons it might be to have splash on mortar fire be penetrative. Not on all cover, just thin things like railings that you can aim up down on. This could work for the plasma cannon,the splash radius should down someone while the kannon would likely kill them outright. As far as the tempest launcher is concerned I wouldn't have a clue, but after facing them recently it seems like their splash and damage is reasonable considering it fires in bursts. The deciding factors of whether or not the splash should pierce should probably be whether or not a player can take standing cover against the surface and whether or not a player can aim downward when bracing on that cover.
It is bugged, less so for Ork Kannon but they still suffer this same problem. Several fortress maps I can't get mortar mode reticle/trajectory to align properly to balconies, even though it should. Often it will either be too short of a shot or jump past my desired target and overshoot by 10' or more. Hopefully devs will fix it across the board how the "Trajectory" arc presents itself in game. What they currently have just doesn't work for mortar mode, most likely because it is tied in with the bouncing reticle issue basic shooters experience. Easiest fix would be to have some mouse wheeling addition to the mortar mode arc from the aiming reticle. In other words initially it is tied to the aiming reticle, but then the player can "fine tune" the arc to get the shot they expect. Doesn't directly fix the issue, but may be a good work around.
