I eventually worked out that with a 90mm deep frame and only 45mm deep door opening outwards like mine - the only way to 'correct' the problem is to set the door "back" in the frame - see Frame / Sashes & Doors / Inner Frame - the 3rd setting needs to be ±45mm. The frame dimension is then the way I want it, but the technically correct way of having the door on the outside of the frame with the reveal to the frame on the 'inside' [because door must open outwards for better weatherproofing] cannot be done [in SA this is a typical building detail]. You are forced to let the reveal be on the outside!
I don't think it can be shown in the technically correct way? I've tried 'flip' and setting the junction at -45 degrees - and I've given up because it's a small compromise that I might revisit when I have more time.
Don't sweat it, because I can live with the innaccurate solution, bugging though it is.