I think it makes sense.
Trade flows according to borders.
The single biggest problem and steering tool for trade in that age were tariffs.
And tariffs are levied by individual princes.
They simply slap enough tariffs on any trade going your way that merchants decide to not go there.
How exactly are HRE princes going to put tariffs in the Ragusa node area?
It makes no sense at all, they have no provincial control, no ships and it's also quite far away from their area (with them having no power projection whatsoever). It's just an arbitrary bonus they get which is multiplied because there's so many of them. Unrealistic as hell.