Have you played airsoft? Because one of the best things about that game is how it puts modern combat into perspective for gamers. I'm just an amateur in airsoft, btw, and I'm not exposed to life threatening RL combat.
From my experience in it, the main difference modern combat has with its archaic equivalent is that you cannot afford to trade blows. It is the lethality of modern combat that makes it more of a contest of maneuvers.
Instead of losing hitpoints, one side tends to lose available options. It is hard and lengthy to explain but if you tried out the hobby I'm sure you'll get how it will work great in a TRPG. Nonetheless i'll try to explain it.
Fog of war is very important in Modern Combat, because one of the basic things I've first learned when I started out was Displacement. From the way my friends tried to teach me, because MC is very fast paced, making sense of the Tactical situation was the key challenge. Having experienced being fired on, I've come to realize there are very many threats beyond the opponent shooting at me. I did not only have to take cover, I had to find one with a suitable position considering my future options, I also had to consider the actions of my allies.
The way it translates into tactical combat is that there will be many Perception + Tactics Checks. Often, these were made to determine and confirm the positions of allies and enemies. To speed up resolution, the GM must filter the information from player to player. Confusion is veil for the players and NPCs, which has a strong influence on their decisions. There could also be other decision influencing factors like time, objectives, emotional disposition and other real life circumstances that always get in the way of everything.
There are a lot of Fright Checks for both Involuntary Character reactions, when circumstances change, and when the character is made to do something very risky. Mob mentality and Panic are infectious and affects combat sometimes strongly but subtlely.
In such a game, for non-military trained players luck and Cp for auto success are very useful. Even combat trained players may need it, just because of the freedom not to risk their own lives in the simulation they may actually take more risks.
Hex grids have to be much larger and represents a larger area then usual. A weapon's effective engagement range is pretty important, terrain is also important (especially when firearms can penetrate many forms of cover), and the availability of information prior to combat can means life and death for the PCs. All because, even before they get hit their options are their HP.
And unlike MANY Computer Games, FP is very important. I remember just getting winded in the first run to cover. It doesn't help that crawling is the safest form of movement (when you are not sure where the enemy is). Panic attacks drain FP for me when adrenaline is pumping too hard when it shouldn't. Communications are also very limited in modern combat, you can barely get a word out if your under fire, too tired, or busy.
Melee combat is pretty clean in comparison to modern combat. Gritty-ing it up with confusion, dispersed positions and the high lethality lends more authenticity. Since Modern Combat is more lethal, giving the PCs a do over at the cost of a CP or two would be helpful and not indulgent at all. The difference between survival may just be luck in many real world encounters.
Well, i don't think a map signaling a fight can be too bad. Admittedly a lot of players get their fun from fights. You can use the map to heighten their expectation by pushing the combat farther down the course of the game.
Combat may be bad if not everyone enjoys them. Here is some of my suggestions to your situation.
Tactical maps, speak volumes instead of having to repeat everything you have to say.
1-Tracking Action Horizon. Modern Combat has a more complicated action system. Typically, you have a lot of long actions, in between short second based turns. Long actions have to be played fast and loose, as it builds up to critical moments. There are many ways to solve this.
a) Use a gant chart to keep track of second-by-second time flow. On a graphing paper (landscape), in the left-most column (up to down) list the relevant parties and NPCs. On the top, list the turns second by second or increments of 2-3 seconds. Let the person taking initiative use it to keep track of the PC initiatives use this, in this method you can see the event horizons of each actions .
2- Maps in Modern Combat, the maps should be represtational of a much larger space instead of 1" to 1yrd or 1m. Depending on the size of your hex map, consider in advance what scale you are using based on the encounters you're planning. Don't feel confined from scale up and down often.
3- Don't let detail bog you down. Fast moving turns are important to a successful game and for the players' enjoyment. Define each area's value in circumstantial bonuses (cover, concealment, elevation, ability to cover an area, etc.). You can doodle the terrain and obstacles without so much detail. You can mark down the bonuses with a post-it or marker if PCs make a successful Tactics-Per check.
4- Markers. Each player has a Marker, when they think they spotted a target, that player may leave a marker on the enemy position. Of course, PC may only attack targets with Tokens of their own, this prevents them from shooting at targets their PC could not have possibly seen.
I would appreciate some feedback on how these suggestions fared with your group. Good luck with your game.
(edited recently to fix my writing mistakes)