Consider a hi-pop industrial system TL11-12, with heavy exploitation of system resources out to the kuiper belt... Mainworld has a starport A or B, and a spaceport or three are scattered among other points in the system. Also assume that in-system jumps are not common.
Micro-jumps (less than 1 parsec) can be done using a Jump-1 drive, but are usually impractical for interplanetary distances of less than 8 days (192 hours) duration on maneuver drive power. It's at this point that I refer you to the
Interplanetary Distance by Time and Acceleration chart to determine how far a ship can get in 8 days/192 hours in one-way transfer orbits to decide if a ship will want to micro-jump or not. Note that a micro-jump round trip will consume 2 parsecs worth of jump fuel for that ship (Jump-1 outbound, Jump-1 inbound) to avoid needing to transit on maneuver drive power the whole way.
How many misjump events, both departures and arrivals, would you expect to occur in the system in a week/month/year? Inbound misjumps would be much rarer than outbound, so we could limit the discussion to outbound jump mishaps.
Misjumps inbound to the system will be rare events.
Misjumps outbound from the system would be dependent upon fuel quality (starport specified above indicates that refined fuel is available), maiintenance status (not all ships get annual maintenance in a timely enough fashion) and distance from gravity wells when jumping. With the type A/B starport for the system, I would expect enough system defense patrols to make pirate attacks an exceptionally rare event (not impossible, but would have to be a unique event). Note that pirate attacks are possible at type C starports and below, which lack enough system defense presence to ward off would-be pirates (per LBB2 starship encounter tables).
So, all things considered, in napkin math terms, I would expect 0.01% of inbound jumps to the mainworld to be misjumps.
Outbound misjumps would probably be in the under 1% range (probably closer to 0.1% or lower) owing to the availability of refined fuel, annual maintenance facilities at the starport and the relative safety of "patrolled space" protected against piracy.
For reference rolling 2D6=12 is a 1/36=2.78% chance outcome on straight dice rolling (in CT) that requires additional DM in order to misjump (unrefined fuel being the most obvious DM). Note that 0.1% is thus 3.6% of the 2D6=12 results ... or literally rolling 000 on 3D10.
Is this number proportinal to dtonnage of interstellar trade going thru the system? Is it significantly affected by the balance of smallship/large-ship traffic?
Not ... really ...
The important thing is that misjumps will never be 0%.
The chances for one can be zero for individual starships, but will never be zero for ALL starships passing through a system (to and/or from).
The greater the quantity of starship traffic, the more opportunities for misjumps there will be.
It's kind of like being a "good driver" who never gets into a traffic accident or fender bender collision with other vehicles ... and yet we can switch on the radio in almost any major city in the world and there will be routine traffic reports of vehicle accidents multiple times per day snarling traffic somewhere in the city.
Small craft cannot jump, so they are substantially "not relevant" to the question of misjump opportunities.
Large ships (particularly the really large 1000+ ton ones) will usually take measures to ensure their opportunities to misjump are minimized towards zero.
It's mostly going to be the "small time" fledgling line operators who can't afford annual maintenance on time that are operating on tight margins with the threat of bankruptcy (and/or repossession by a bank) and thus don't have the reserves to keep up their annual overhaul maintenance that are going to be the misjump risks, even with refined fuel. The quantity of starship traffic that falls into this "low end and poorly maintained" category is going to be the most likely culprit for why misjump chances cannot ever get down to zero.
So the number of misjumps per week/month/year are going to be highly context dependent upon the types of starships, and the upkeep of their maintenance schedules, that will be arriving and departing from the system. More starships passing through, more dice rolls ... so in that sense the interstellar trade quantity is relevant, but the tonnage quantity should not bias the percentage chances for misjumps all that much (high chance for lots of traffic, low chance to nearly no traffic, is not the way it should work out). More like the "clunker/junker" starships are the main risk factor, so the more of them in the traffic pattern the higher the overall risk for misjumps.
But what would the In-System Traffic controllers expect to see in their system?
Honestly ... with a type A/B starport the starport controllers would expect to see a lot of ... compliance ... with their orders over comms.
For those who don't comply, the "space lanes" ought to be patrolled well enough by system defense to "compel compliance" if craft (large or small) fail to comply with orders from starport control.
