Dear all,
1:
I suggest these four systems not to be exclusive but complementary.
Each would measure quantities of information on the target.
Enough information allows us to calculate its distance, velocity, and acceleration.
That is lock-on when you have them as it will allow you to fire were the target will be based on recent measurements.
Of course, a target can change course during the time of flight of your ordinance, that is acceleration.
If you are going to the radar cross-section, you can consider the whole link budget https://en.wikipedia.org/wiki/Link_budget.
That is still spreadsheet level (first rough estimation) calculations after all.
It would consider the radar emitted power (after antenna gain), distance, reflected power (that where cross-section impact), return distance, reception gain.
The advantage of bigger vessels is to emit more power and have a bigger antenna array (that is better antenna gain).
Meanwhile, the advantage of a smaller vessel would be the lower cross-section.
That is for radar, where you illuminate the target.
But on the thermal side, you have to look at the emitted power (EM radiation) from the target exhaust flare, return distance, reception gain.
After that, you can do an exciting thing if you suppose you have excellent thermal isolation that allows you to survive in a minimally powered, cold vessel.
Then you are cold (not emitting power), stealthy (low cross-section, you reflect little power).
Gravimetric detection will be useful to detect your hiding vessel.
However, a capital ship looking for you would be emitting power with its radar making it easy for you to see it in return.
Finally, it would be the ship designer choice to install all the four systems and spare the space for the antenna/telescope size (basically, a telescope is a reception antenna in the visible specter)
Please do not consider my following citation as publicity. I am not working for them, nor I believe them competitive to Dual.
To acquire insight into targeting mechanism, I would recommend the following simulation game.
3:
In ballistics, nothing fire in line, everything fire in a cone.
Even if a cone is very narrow, the precision naturally degrades in distance square (imagine a more extended cone that keeps constant its angle).
It is different, but similar to the laser that sent the light over the whole cone.
Thus, the laser focuses the EM power on a small surface at close range, enough to do thermal damage.
A long-distance, the laser spray the light over square meters and become virtually a, not even warm spotlight.
To acquire insight into realistic space combat, I would recommend the following simulation game.
All of it is still at the spreadsheet level.
Best regards,