I would increase their speed up to 277 meters per second once they achieve 100-200 meter altitude and come down. The only way to buff direct fire is with the use of TAG/Narc/Artemis.
Direct Fire Mode: LRM spread is larger then indirect fire mode and can't go around intervening terrain. Basically, they lose their homing ability and can be stopped by terrain as it is a straight shot. The internal guidance cannot act fast enough to maintain internal lock on the target.
Indirect fire: Ignores intervening terrain, except for caves and other rock formations that cover the top of the enemy mech. Spread is tighter due to the missiles' guidance system being able to compensate for them while maintaining a solid lock.
Locks are not mandatory for indirect fire mode since these are guided munitions, but they are needed for direct fire mode.
EDIT:
Time for some numbers.
Range BTH* Spread
180-270 30% 5.2m
271-370 35% 4.7m
371-470 40% 4.2m
471-570 45% 3.7m
571-670 50% 3.2m
671-770 55% 2.7m
771-870 60% 2.2m
*BTH=Base To Hit
This makes LOS indirect fire at close range to be inaccurate while long range indirect fire more accurate. It also allows for Narc, TAG, and Artemis to affect the BTH positively.
Edited by James The Fox Dixon, 02 June 2017 - 08:58 AM.