My main issue with your changes are as follows:
1. You have movecost = $gameMap.terrainTag(dx, dy);
I believe this should be movecost = _terrainCost[$gameMap.terrainTag(dx, dy)];
If you use your method, the movement cost of terrain is equal to the terrainId
But in rangeControl.js, there are plugin parametters that allow you to set movement cost of terrain which means terrainId of 3 may have movement range of 1 not 3.
2. Your change breaks moveTable compatability; which means if I make a change to srpgPathfinding.js to accomodate your changes, it will break compatability with the default moveTable method. I have applied a temporary fix by adding a new plugin Parameter to my plugin.
For those out of the loop, I have attached a picture to explain the changes that ShouKang has suggested in his edit to rangeControl.js:
I personally agree with his changes and will in the future be incorporating his style of movement into consideration