Let's face it: the SM fleet is not well designed for long range combat. It suffers from very low lance counts, average range and many bonuses that are only applicable at close range, such as boarding and hit and runs teleports.
Their strengths are their bombardment cannons, which are ludicrously destructive at point blank. The thunderhawks, who although small in number are very versatile and obnoxious to kill. Their maneuverability and speed, which are higher than human average. And their resilience, which is close to the highest in the game.
Check out Seahawk's winning fleet from adepticon last year (or the one before?).
Master of The Fleet
Optimus Opprimere Battle Barge
3 x Strike Cruiser w/ Extra shield and Bombardment Cannons
3 x Strike cruiser w/ Extra Shield
Simple and brutal. As you can see the fleet utilizes its ordnance to launch pre-preemptive attacks and ward of enemy bombers whilst closing, and then catches the opponent in a withering crossfire of over 30+ strength of bombardment cannons.
Your choices increase the range of the fleet significantly but water down its primary focus. Problem is, at least on paper your fleet is not especially good at either form of combat any more.
So you need to look at what is causing the problem. You have two non-SM standard vessels, your nemesis and the mars. The nemesis gives you the most t-hawks on one vessel possible, but you lose out on any significant firepower. IIRC, it only has an average lance or battery on it. And since it is helpless up close, it will have to stay back from your main fleet, meaning it's AC will have to travel further making less relevant and useful. You would be probably better off with an Emperor in that role, if only because at least it could fire a useful quantity of batteries from it's backstage spot. Your best option for this role is probably a despoiler battleship, as not only does it have strong ordnance but it can put out a strong torrent of long range battery and lance fire to support your fleet. The Mars I feel is probably the biggest culprit, however. It is your only Nova Cannon and is thus unreliable, and even with the new BFG:R lock on rules it will hardly benefit due to its need to reload ordnance every turn. It's batteries are not strong enough to really contribute once it closes, and it's paltry t-hawk contribution is not really that useful when a basic strike cruiser provides as much. As Dan mentioned you more likely to get mileage out of the Armageddon, and you can even keep your single Nova if you want because few ships lock on as frequently as the Armageddon. Another solid choice is the Dominion from battlefleet bakka, which will save you a few points and provides more lances than the mars.
If you hypothetically swap in a despoiler and an armageddon (torpedo version), you would lose out on a NC and 4 T-Hawks, leaving your total at 4+2+2=8, a pretty respectable amount for SM. But you have gained significant ranged firepower (2 lances at 60cm and 2 lances and 6 battery at 45cm from the armageddon, 10 battery and 3 lances from the despoiler) and tightened up your fleets overall effectiveness.
If you took the armageddon, you could consider swapping your bombardment variant back to stock to shore up your ordnance capabilities. You could also shrink your thunderhawk size by one to add a str9 torpedo volley from the despoiler. That's a pretty good bargain IMO. If you took a dominion instead of a mars as, you could probably afford to convert an extra strike cruiser to the bombardment version for that extra close range punch.
No matter what you do, if you save enough points here and there (looking at you, terminator and honour guard
) you could and should throw in more hunters, or a small nova squadron. Both rank amongst the best escorts in the game, and a 5 man hunter squadron will be a massive headache for your opponent due to their striking range.
Hope this helps, feel free to do your own thing if you disagree!