In the base game the rules for the Tractor quality are basically this: If the attack is successful, the target must make a piloting check equal in difficulty to the Tractor rating in order to move.
I find this insufficient because that would mean that, for example, Slave I could hold a Star Destroyer in place (Tractor 2). Given power generation (Slave I), inertia (ISD), shear brute force engine power (ISD), levels of system strain (ISD), etc. I find this insufficient. I also think that the difficulty is insufficient for ships attempting to escape (more on this in the proposed solution). For example, an ISD trying to escape Slave I's Tractor beam (to follow the example from earlier) would face a difficulty of average, however, a Gozanti (same speed) would face a difficulty of average as well, even though it would fit inside one of the ISDs thrust nozzles (the smaller ones). Needless to say, I find this lacking.
My proposed solution is as follows: Tractor beams can grab onto a target of a silhouette equal to or less than its Tractor Value (see paragraph 3, line 4). The pilot must pass an appropriate Piloting check (or athletics if it's a person being targeted) at Average (2) difficulty increased once for every point of silhouette short the target is of the Tractor Value (see paragraph 3, line 4), upgraded once if the target's strain exceeds 1/4 threshold, twice if the strain exceeds 1/2 threshold, and cannot be attempted if the strain exceeds 3/4 threshold, but subtracted by max speed divided by 2 (difficulty=2+(Value-silhouette)-(max speed÷2 [round down). I would also change the Tractor values to: Value=Rating+(Silhouette÷3[round to nearest]). So an ISD targeting Slave I with a Heavy Tractor Beam (Tractor 6) would be 6+(8÷3[rounded])=9, leaving Slave I with a difficulty of 2+(9-4)-(4÷2)=5. This represents all the aforementioned variables: (1) Target: Inertia (silhouette), engine power (max speed), System Strain levels (die upgrades). and (2) Attacker: Power Generation (Silhouette). Also, any overflow in difficulty (anything greater than 5) would go into upgrades (6 difficulty=5 difficulty, 1 upgraded).
In conclusion, for everything I have calculated so far, this is balanced as it allows small ships (silhouette 4) to move cargo and starfighters (Light Tractor Beam [2]) medium ships to move cargo and small ships (silhouette 4 and smaller) and some ships of similar size (Medium Tractor Beam [4]), and large ships to move all of the above (Heavy Tractor Beam [6]).
I would welcome any suggestions or critiques.
P.S. The equations on their face may look daunting, but they are really rather simple, I just wanted to convey the information in the most precise and formulaic way possible.
Edit: P.P.S. You can't attempt to escape unless you are moving in the opposite direction of the pull of the Tractor beam or faster than the chasing ship (if they are trying to reel you in while moving toward you, you count the targeted ship's speed as 1 lower).
Edited by P-47 ThunderboltAmendment (P.P.S.), 9/3/19 clarification.