First off those plants look fantastic. I started out in Coco growing with the 3 part by advanced nutrients paired with Botanicare CalMag+. Definitely solid results.
I would make sure you stick to your feed chart, never slack on CalMag always apply it, especially with the non coco specific line of nutrients like the trio (perfectly fine) and honestly watering until runoff is important but you dont need lots of run off especially with AN its pretty clean stuff as in it doesn't have tons of salts and stuff in it that is going to clog up your coco.
I'd keep doing what you're doing though it seems to be working.
How can you tell if you should raise or lower you ec
You can achieve knowing to feed more or less by monitoring the plants visually. I've had really good luck just following Advanced Nutrients feed charts throughout the plants growth. I used to run AN start to finish 2 oz per/5 gallon of water of each part and 20 ml per 5 gallon of water of CalMag. I want to say that brought my EC around 1.4-1.6.
When the plants are small you should feed around 1.00 EC then as they get larger you can ramp the feed up to as high as 2.0 EC unless you start seeing burn or something and then just pull back. You can always add more you can't take away so always increase feed as the plants grow in small increments and monitor the plants or take pictures to track results. Log everything on paper or in a note app.
Here's my guidelines with feeding coco with liquid fertilizers.
Early Veg: 0.5 EC
Mid Veg: 1.0 EC
Late Veg: 1.2 EC
Early Bloom: 1.2 EC
Mid Bloom: 1.4 EC
Late Bloom: 1.8 EC
These numbers can change depending on genetics though. For example the Gelato 33 that I'm growing needs LOTS of CalMag compared to my other plants. As much as 10ml/gallon of water, no kidding at all...
Also, keep your PH around 5.8 in Coco if possible, unless you're running the PH Perfect line of Advanced which in that case you do not ever need to screw with PH, ever.