In my opinion, theres one formation that works the best, and is the most safe. In the case that you went arboreal path, this is probably the safest way to solo. Face the group of mobs you want to destroy (bwahah :D) and then put your controlled shroom in front of you. This will be your shroom for pulling. Behind you, keep your FnF (fire and forget) shrooms far enough away from casting range from teh group, so they don't pull when you're not ready. Make sure they're still in range of the controlled turret though. So, you pull wtih your controlled shroom and your little mobby comes to attack it, then your FnF shrooms open fire. It works pretty damn well for me, I can burn through a whole group of like, yellow-orange in about 4-7 minutes. Maybe less. Hehe. Just rest while your pets do the work... Although this strategy is effective, its quite the grind. So... Bleh.
THe most important thing is to experiment, try new things, if something doesn't work out, you've learned from your mistakes and you can move on to the next idea. Find a style or formation that suits you.