Lots of fin range is a double edged sword as one can get overwhelmed with choice and what conditions to use what fin/location, and set up in.
My opinion, if you are designing a twin with a trailer, then use the general accepted twin placement/cant/toe in, and have a few different size trailers, going bigger and rakier as the waves get more powerful. If you want it to be able to ride it as a true thruster as well, then see if you can cram another box forward of the twin boxes, but I think it is a mistake to think a thruster rail fin position makes a valid twinny, or a valid twin fin location translates to a thruster feel, and splitting the difference could work, or perhaps will be the worst of both worlds. Lots of archer not the arrow possibilities, and personal preference too.
If you can make your own fins, you can move the tabs forward or back to relocate them in the board, though futures and especially fcs2 does not make this an easy option.
I was steered towards Probox Hawaii for ease of fin tab making, and the fore/aft/ cant adjustments, but the amount of choice can be overwhelming. I carry a fin key, sewed a zippered twinfin sized pocket into the thigh of my shortjohn wetsuit and often flip the board over sitting in the lineup, and adjust/swap fins or canted inserts, just to see what they do on the same day/location/swell. It’s pretty amazing how much different the board feels moving the trailer fin fore or aft 1/4" or less, and one rail fin can often find itself moved all the way back and the other all the way forward with 6 degrees of cant on my forehand rail and 8 on my backhand.
One board I designed in mid 90’s I had 4 fcs plugs all touching each other for both twin and thruster postiions, but while the thruster position was solid, the twins were not toed in enough or far enough back or something. I wound up using it as a twin with and without trailer about 5 times, not clicking with the board, moving the twin sized fins to thruster locations during the session where they felt better, before removing the grubs for the twin locations using it forever after as a thruster, changing center fin size with wave size.
I just don’t think a universal twin/thruster/ rail fin position can be done right, without designing the entire board around that option, but that’s my opinion, and certainly not fact, and I know not how to design the board around that option.
I believe most twins trailing edges from the days of old, were 1/4" or more farther from rail apex than thruster fins of today. I think the recent MR twin thread was 1 3/4" from rail apex, but it could have been from the edge of the tucked edge.
https://www.youtube.com/watch?v=TF55GZugWEo
This video^ shows Mr’s twin fin positioning process.