I know this is an old chestnut but I need to revisit gear and brake cable routing when used in conjunction with a swept bar and a Lion harness. Last time I cabled gear and brakes on a loop bar I left the cables long but not long enough and ended up with either a tight squeeze with the bar bag behind the cables or the cables deflected over the top of the harness which I seem to remember caused the back brake to rub. My new frame routes cables via the down tube not the top tube which may be an easier route with a bar harness. The H-bar always looks as though the cables could be routed cable tied or wrapped along the front loop but then I can’t see the transition from bar to frame especially with a harness other than sufficient loop/slack to deflect round the back of a harness.
Missing a frame and bars at present or would do my own experimenting just wondered if anyone else has tried various set ups and established what works and what does not. Maybe sleeving or ty wrapping gear and brake cable pairs together to save having four cables flapping about in a huge loop out the front?
Re the Lion harness. Has anyone modified the method of attaching the harness? Not used it for a while but it always seemed a major thrutch getting everything tight and in the right position using a single strap for top and bottom each side. I did ask about modifying mine to give a top and bottom separate fixing loop but there may have been a technical reason why this could not be done. Probably cost knowing me.

What sort of bars? Can the cables not be 'trapped' behind the harness?

I know it’s not necessary what you want to hear but you probably need to wait.
The best results i’ve had with various bikes bars and bags is routing the cables with a loaded bag attached to see the best way forward.
Each time the solution has been different.
One word of caution with this approach is that you can end up with slot of excess cable if using the bike minus the bar bag. It pays to check what it’s like unloaded as well before you cut everything and finish the job.