Given I've seen shots come from outside sensor range, I don't agree. I actually think the sensor contact part is one of the more interesting periods of an engagement.I am thinking the sensor range is either too big or shows too much information (such as mechs' tonnage) - it removes the element of surprise, because you know, more or less, what you're facing, even if you don't see it.
Its time to start taking advantage of terrain and maneuver and decide if and how you want to engage. Fall back to allow slower mechs to move up into a firing line, or form a pincer move to cut them off and isolate the enemies out of range of static positions.
One thing that would help the element of surprise is the objectives not telling you when there are reinforcements and how many enemies you need to kill (either directly or by percentage)