You are probably right, but that would mean that my training so far has been too hard since I have been on Quarq/Kickr powermatch for almost a month now. Although it felt all pretty manageable (just VO2max which was really really pushing it, but that is also the nature of these intervals I think).
Also, if with the Quarq as a standard now (FTP 279 with ramp inside vs. >350 W for close to 8 minutes outside seems a very big discrepancy). I know inside can be a bit lower, but 30 watt difference is a bit too far off.
So considering all the replies (Thanks so much!) most likely it is a combination of factors (outside being generally higher, changing from Kickr to Quarq as powersource (although both measure very similar if I compare side by side), too close after a hard ride (thus some fatigue), and maybe some other factors (mental: motivation, distraction. Physiological: bit low on blood sugar, Mg/Ca ions, vitamin B/hemoglobin etc. that always fluctuate a bit).
I think considering everything, I take it a bit easy for now, pick up the scheduled training with my old FTP and see if that feels right and test again in the near future without powermatch but with dual Kick/Quarq recordings.