First things first: Bridger plz move to MM forum kthx. 
Secondly, if you find that your Mercs are only firing off certain weapons at specific ranges - can't say for sure if this is true, as I've not had a Mercs/ MM that high - then you might want to make liberal use of the placement tools available to you as an MM; specifically, using the /petcom and goto commands to move your henchies into and out of range.
e.g.
/petcom_all goto - Moves all your pets to the selected position.
/petcom_pow Commando goto - Moves your Commando to the selected position.
/petcom_pow Spec goto - Moves your Spec Ops to the selected position.
/petcom_all goto def - Moves all your pets to the selected position and puts them into defensive mode.
/petcom_pow Commando goto agg - Moves your Commando to the selected position and tells him to go nuts.
/petcom_all follow def - Returns all your pets to bodyguard mode.
Everything you've suggested is available to you already - you just have to do it manually, as opposed to it being done for you.
@Synaesthetix
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it isnt just merc there is slight problems like that across the hole mm AT fir instance with thugs your bruiser who is basicly a mini brute will refuse to enter melee range choosing to nstead stay at range and use hurl over and over the Assault Bot on roobots has the oposite problem sometimes chooseing to enter melee range and jsut slap somethng to death when its build for range carnage
the comands to set the pets to do this manuly do help a little but i think your right there AI and power use/choices should be a lil better than what it crently is
There isnt a problem on earth that cant be solved with the proper aplication of hi explosive's
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Actually, this is an overall AI issue, and not specific to masterminds. EVERY AI-controlled NPC follows that line in combat. Mastermind pets are unique in that you can order them around, and therefore alter their response slightly... Controller/Dominator pet do the same things, only you can't do anything about it.
The good news is, of course, that the enemy NPC's ALSO act like this, which you can take advantage of.
For me the Spec Ops and Commando almost never use thier snipes, unless the enemy runs away or Position them far away. The Commando also never uses the Flamer unless I move him close.
I'm fairly sure they like to stand still, and use the attacks that fit that range, annoying as it means you have to move them about to get the good hits in >.<
I tend to re-issue the bodyguard command, or force them to a spot with the goto command, as you risk one or two of them not doing much at all, left to their own devices. At least one of them seem to lag behind when you move a lot, and can be found eating popcorn and enjoying the show from a safe distance. ;-)
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I've noticed recently with my Ninja/TA MM.
I use smoke flash on my jounin, which equates to roughly a 10 second window of constant crit ability - he can pull off all his attacks in that window nearly.
Yet he insists to run up to them, wait 2 seconds. Cast Placate. Wait another 4 seconds.... Use Gamblers Cut.
Good move...
To be honest they should actively compare recharge times of powers and time left till recharged to calculate when a power will be ready, and if there will be a higher damage one available. Also maybe some comparisons between current range and next closest range power to see if they should close the distance. I hate seeing my Spec Ops stand at a distance sniping, when they have a load more attacks up theri sleeves.
for masterminds mercs/###
Do your mercs seem to be choosing weaker attacks over the more higher damage attacks available?
Why is my commando picking buckshot over slug.....
Why burst over the LRM....
It seems Mercs are configured to fire off weapons at specific ranges, not when they're readily available.
Perhaps they should be made to fire off attacks in damage order, but also only attacks available at their current range.
Like at point blank they'd fire off the highest damage attack (LRM) followed by the 2nd highest (SLUG) and then the third highest etc....
But at long ranges it'd fire (LRM) and then get closer in to use the rest of his attacks rather than sit there blankly waiting until LRM is recharged...
I.e.
At long range, fire off long range attacks and proceed to close to medium range.
At medium range, do not advance. Fire off all available attacks.
If at close range (do not advance to) fire ALL attacks starting with highest available.
how's that sound?