Unfortunatelly and especially with the whole analog rig always exist trade-offs.
If it's real that a longer tonearm has lower tracking error it's true too that the cartridge/tonearm alignment must be super accurated because a minimum inaccuracy rpovoque even higher errors that in a shorter tonearm. In the other side in a longer tonearm the developed resonances/distortions are higher than in a shorter one.
With linear trackers exist trade-offs too like the opnes you named and others and one of those " others " is in the bas range ( specialy inl low bass. ) where almost any pivoted tonearm but unipivots are second to none and superior to the LT.
Now, those inner grooves compromises with a good analog rig and a high resolution system as your can be put at minimum where you can't detect it for this you need a good damped tonearm and a a cartridge with good tracking habilites. I don't know if the 312S comes with a trough for silicon oil damping as the SME V, this helps to better tracking and lower resonances.
Now and even that your cartridge/tonearm frequency resonance has no problem your cartridge is a low compliance one and bad tracker that shows normally at inner grooves.
The tracking error in the SME and other tonearms is really small for been or develops that problem. I that been the problem then the 98% of audiophiles that use pivoted tonearms always have your problem and in my case in the last 10-15 years I left to have that kind of peroblem. LT can't fix it because the trouble is in the cartridge maybe only the one you own not all SS Susorro samples.
I have several cartridges that runs in pristine way the Telarc 1812 LP that is the most extreme challenge at inner grooves.
So, I think that your problem is not exactly at the 312S but somewhere down there.
If you want to go a head with a LT then could be " healthy " to test it before buy it at your place with your cartridge.
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.