Having a way to lock the rifle onto it is the easiest improvement. But some of the NRL guys seem to like dropping a sandbag on top so there's probably something to that too. I don't have any experience with the spartan systems. I went arca on my stuff optics and rifles so i can drop any of them onto any of the tripods I have. Have your attachment point as close to the rifles balance point as you can live with. I do mine just in front of the mag well leaving a little space to carry the rifle at the balance point without having to grab the arca plate. If your attachment point is close to the rifle's balance point you can lock the rifle into the tripod and leave it there ready and waiting for you with minimal fiddling. I set up the big tripod and lock a rifle in when I'm cleaning the bore too.
Ball head so you can level the rifle without having to fiddle around with the legs. Keep the column all the way down or nonexistent. More weight more higher is more unstable. And the greater % of the tripods weight capacity you are putting on it the less stable it will be. Same goes for your position you and the tripod both being lower is more stable so if you need higher go for as much as you need and to have a good position and not much more. Along with that on a three plus section tripod leg when extending for more height extend your thickest legs first.
If you are going to have multiple tripods the biggest/ heaviest / highest weight capacity one in it's shortest configuration that meets your needs will be the most stable. Of course that has to be balanced against bulk and weight to haul it around and how much stability do you need/want for what you're doing.
For my glass tripod an azaik backcountry lite I have a pan head for glass on the long column and a ball head for shooting on the zero column. 6oz and a quick swap and its much better to shoot off of. I like simple controls on the ball head one big lever that does lock and unlock. People can get good with the ones with separate knobs but I went for only one thing to deal with.
I also put hockey tape on one leg of my tripod so if my left hand feels the tape my lock/unlock lever is just up there above my hand. So I know where my controls are without looking down and around for them.
Now that your rifle is stabilized on the tripod you want to position yourself so that you are stable. Sitting with my back against something and a pack in my armpit of my dominant arm/hand is the best I can do from a sitting position. I'll try and get my legs arranged so my knees or thighs can contact my dominant hand elbow if I don't have a pack to do it. Sometimes I'll get my feet wrapped around two of the tripod legs and pull it toward me a little. I'll often hold the tripod head with my non dominant hand. But more points of contact for rifle, tripod, and you will make things more stable.
Dry fire helps and is an easy way to try out position arrangements and different position heights. Pick an object in the distance and see how steady you can get on it to dry fire. If something seems good try it at the range or shooting in field condtions next.
