Would this really make that much of a difference?
If your regular Ampere are less than 100 Amps in/out, then I expect no difference on a 350Amp rated shunt.
btw, the AiLi 350Amp Shunt that i have actually says 500A on the metal. so they sold it advertising 70% of the max rating.
it could probably take 500A but for a short time.
if its running at 350A all day then it could heat up. main undesirable side effect might be: heated up shunt report inaccurate Amps by some percent
100A or less on a 350A rated shunt should be fine.
disclaimer: i'm amateur. 500A*70%=350A so 100A would be only 30% of the 350A number which is supposed to be ok. hope this helps somewhat.
in an extreme case, the fins being oriented flat will result in less convection air cooling the shunt, like 300A+ for hour or more, then the shunt would heat up and report some percentage inaccurate Amp measurement
but in this case i doubt it will become an issue until a lot more stuff is added and running constantly.
usually shunt makers try to make it out of materials that do not change their properties much when temperature change. like how rubber becomes hard cold soft hot, but with electrical resistance instead
