I'm curious to see how a 4/6 is "outrunning" a 3/5. The max TN it can generate is a +2, and it does this mutually. +2 for the attacker and defender. How is that an advantage for the 4/6, who now has a worse heat curve and/or less firepower? ???
It can generate even movement modifiers (the same value for shooter and target), and still turn a hexside, move up or down a level, or step into a forest. If you can get a 'Mech set up to pace back and forth between two Light forests, with two hexes of open ground between them, it has an AMM of +1, while enemies have to deal with a TMM of +1 and a Light Forest, for a total of +2. Because To-Hit rolls are on 2d6 bell curve, this means that although you are losing effective firepower compared to being stationary in a light forest, the enemy is losing more.
*****BEWARE, MATH BELOW*****
G 4, LR (+4), To-Hit 8+ (.41). Enemy G 4, LR (+4), Light Woods (+1), To-Hit 9+ (.28)
The ratio of your hits to his is (.41/.28) or 1.46
G 4, LR (+4), Walked (+1), To-Hit 9+ (.28). Enemy G 4, Long RR (+4), TMM (+1), Light Woods (+1), To-Hit 10+ (.17)
The ratio of your hits to his is (.28/.17) or 1.65
Stationary in a forest, any design will inflict 1.46 the number of hits on a target that the target will inflict back (assuming the target generates even movement modifiers, which most 3025 Heavies do). Walking 3 into a Light Woods (which a 4/6 can do but a 3/5 cannot), you will inflict 1.65 the number of hits.
Before you say that having two light forests with two hexes separating them is an ideal situation, the "Battletech" Mapsheet has that exact setup in two different locations.