Every Mech have a primary configuration. However, all these configurations are set with weapons to have an advantage at a certain range. It's a good idea if you have leftover resources after you buy and sell Mechs, etc., to customize and play with different configurations set with weapons for all ranges of combat. The Mechs will not fire long range weapons at short range. You cannot set one Mech with long range weapons and expect them to fire from long to short range. If you do this and the enemy has shorter ranger weapons and is faster, it can easily run within the range of your weapons and take you out. Long Tom cannons and Swarm LRM racks focus devastation on a wide range effect area rather then a focused point. Make sure your allies are not near an enemy when these long range weapons are fired. Also with Mechs, when they are completely destroyed, their nuclear reactors explode. However, unlike the original Mech Commander, the explosions can damage you. Any of your troops near a Mech when its reactor blows will get damaged, or if they are right on top of the wreckage of the exploding Mech, they could be killed on the spot. This is what makes close range combat dangerous. Most Mechs usually move away or move to the next target before the enemy Mech explodes. Immediately move those that just sit there.