I'm building up a 2015 Salsa Colossal Ti with a full Ultegra 6800 groupset (though with the RS685 hydraulic shifters). I'm having an issue setting up the front derailleur. I've followed all the various tutorials online, but whatever I do, I can't seem to get the cable tension right. Too little tension and I can't get the derailleur to hit the high limit screw. But when I add the necessary tension, then the derailleur won't hit the low limit screw. I either have chain rub in the 50/11 or in the 34/32.

I even have the little plastic tool that tells you whether the converter should be on or off (off in my case). Out of desperation, I've tried the other converter setting, but no luck.

The factory built bike from Salsa comes with the same Ultegra components (apart from the RS685 shifters), so I know I should be able to get this to work. Am I making some rookie mistake?