For a civilian shipping delivery that starts and ends in the same system, the shipping line pays tax equal to half the single-hop amount.
This is too much.
The typical distance between large populations in a single system is much less than half the typical distance per hop between large populations in separate systems.
It's probably closer to one tenth.
As a result, the number of easy colony locations in your starting system has an outsized impact on your wealth development.
Systems like Sol, which have multiple low-cost, easily terraformable colony prospects, generate so much early wealth via civilian shipping that the player's strategic decisions for the entire game are only very rarely impacted by wealth concerns. The player gets rich fast by developing those home system colonies, and then never has to worry about wealth again.
If you start in a system without easy colony prospects, you don't enjoy this early source of easy wealth, and as a result you actually do have to manage your spending wisely, and devote non-trivial research and production to increasing your tax income.
I suggest dropping the intra-system civ tax to either 10% or 20% of the single-hop rate.