Elite Smart B and Garmin Vector

Hi, I am using an Elite Qubo Digital Smart B turbo and Garmin Vector Power Meter with zwift. I use the same set up with trainerroad and in erg mode it reacts exactly how I would expect - must admit I haven’t tried a zwift training session. I am 62 kg and ftp of 160. I have set the “difficulty” setting to max in settings. All output seems OK, eg cadence and power. But I have to use quite a high cadence 85 plus and the top gear to get power at say .8 of ftp on the flat. On the road I would have an average cadence of about 70 - 75, which I appreciate is a bit low but I only came to serious cycling in my late 60’s. On gradients say of 6% I still need to be in top, my speed drops, and the power goes up but it doesn’t really feel like a hill. A 6% climb on the road would require me to change down and my cadence would drop. If I do change down then my power drops a lot. Is this a normal experience or have I set up something incorrectly?