Well, that all makes sense, except for the bit I've emphasized. A vessel covering one world is not going to regroup with any vessel covering another world in any time span that makes sense. However strong the individual vessels are, that's the strength the squadron can bring to bear in any one spot unless they're bunched up.
Mmyes... it's certainly what canon tells us is a viable strategy. Lurk deep down a gas giant's atmosphere and strike against much bigger ships when they are trying to refuel. Personally, I've always had my doubts about sensor coverage and just how much of a gas giant's surface a refuelling ship traverses.
You need a vessel per fuel source to cover the entire system, but if one of those sources are more popular than the rest, you can just cover that. Or the X most popular, where X is the number of vessels you have.
If a legitimate merchant knows that a particular fuel source is being covered by legitimate military forces, it will use that one. If it doesn't know about any protection, it will choose a fuel source randomly and cross his fingers.
(Unless he plays it safe and carries extra fuel along in the cargo hold, in which case he won't get anywhere near an uninhabited system.)
Hans
Ya know I like it when people make me put my thoughts in some sort of order, and answer questions

Part of refining my ideas.
When I did the picture I envisioned it as part of a roving patrol, or sent to a system to deal with an uptick in hostiles, or raiders. possibly a tripwire force to detect, deter, or destroy scouts, or probing forces.
In open space, yeah intercept would be problematic if the enemy can jump. But if it's not able to refuel, or has extra fuel on board. then no matter what it has to deal with the ambush force, or surrender. Taking the long way round to the next system is not an option.
Since an enemy which cant jump away is cut off from fuel sources. the patrol group isn't as pressed for time. It might take days, with a detachment near the ship standing guard to keep the target fro refueling, and the rest of the patrol moving to form up and attack in good order.
If the target is strong enough to engage the patrol group directly it might end up in a force on force fight, or it might attempt to drive off the blockading detachment and refuel. either option gives the patrol time to get into combat range...and with a spinal mount on the cruiser it can deal a lot of damage to exposed escorts while it maneuvers to engage the enemy heavy.
Since a cruiser would have several frigates and/or, destroyers, and corvettes along as escorts. An enemy getting boxed in becomes more likely. a single ten ship squadron would be enough to control a system. Add to that fighters drones, remote sensor packs etc... a system turns into a very crowded place for a hostile force real fast.
to cover multiple fuel sources you can post a corvette or frigate at each one, loitering deep down, or on a nearby moon. it doesn't take a lot to disrupt a skimming run, since you have to fly straight level and true any decent shot can light you up with a swarm of missiles, and particle beams.
Even if it only takes a couple of hours to scoop up the raw gas, it still takes a while to process it for use...and a day or more is a long time to be lingering around with a force backed up by a cruiser making best speed to intercept.
As for merchants and known patrols. yeah, a known defensive squadron would be a magnet for merchants, and a massive deterrent to anything preying on them.
I can see fleets deploying ambush patrols near systems that are not normally garrisoned, as a further deterrent to anyone who isn't there for legitimate reasons.
a garrison force would be out in the open screaming hey Look at me I have big guns, and you cant get to this lovely gas giant behind me...an ambush patrol would be operating in the dark. Hiding near points of interest/value, and doing everything they can to avoid detection.
The worst they could do is get spotted an spook the target which runs away without causing any harm. and the system gets tagged as being guarded.
Either the Target withdraws and runs home for bigger guns, which gives the defenders time to send for reinforcements. or it leaves and never comes back. Either way the patrol has achieved a sight advantage.