I'm not sure we need to get into that much detail. I think the simpler solution is better, with the understanding that the bonus for TL8+ is due to the exploitation of the mineral weath in the entire system, not just on the main world. E.g. TL0-3 +0, TL4-7 +1, TL8-9 +2, TL10-11 +3, TL12-13 +4, TL14-15 +5.