Bremen beat me to it, these changes don't do anything but add micro. Same goes for boost, if the slower fleet kicks on boost but can't fight, its not helping at all, and if boost becomes key to beam combat, everyone will just bring boost. So if your boost is fast enough to outpace the otherwise superior enemy, they'll just kick on their superior boost and now its back to the same problem, except nobody can fire their guns without chilling dead in the water for a while. I guess its good for running away?
I'm still not entire sure why we're trying to create a complex system to resolve a problem that has already been solved. The beam knife fighting problem of minor advantages being an all or nothing win was already solved with the implementation of missiles, you are supposed to use combined arms. A modern guns only warship would be shredded it it tried to face down a faster opponent with longer range on its guns, and the solution was cruise missiles. Beams are supposed to be secondary batteries, and the risk to using them instead of your missile armament is being at that disadvantage to your enemy.
The only thing I can think of that doesn't involve ridiculous amounts of micromanagement, while also stopping the worst of beam kiting, is have it based on direction. if you opponent is within a given angle from your rear (based on your movement that turn) then you suffer a range malus for firing into your engine wake or something technical like that. Superior opponents will retain their speed advantage, but can't fire as far directly backwards. This means you can't just fly directly away from the enemy and use the full range advantage, you need to either go oblique, or turn into them, both of which give an inferior enemy a chance to close. If your speed or range advantage is so overwhelming that they still cannot deal with it, that's fine, such a massive tech difference should cause problems.
Edit: On retrospect, I'm not even sure that'll help, you'd just make larger laps of leaving then closing the range. I still think the solution to this problem is "Bring missiles"