This is my slim fit trouser...

[Hendrick]

Hi, like Peterla said, try pre-setting the curve first befor you alter it. Your trouser is sitting reasonally high at the center-back already. So if you deepen or hollow out the curve they will crawl up higher and they will stick against your front thighs...

[GipsyApprentice]

Hi, like Peterla said, try pre-setting the curve first befor you alter it. Your trouser is sitting reasonally high at the center-back already. So if you deepen or hollow out the curve they will crawl up higher and they will stick against your front thighs...

Thanks so much again Maestro, I did what Peterle pointed before and either lowered out a bit the curve, and the result is this..:






...I think that it looks more correct than the attempt before... And now ironing the legs and do the hem seam...

[posaune]

Very well done!
If you want to go further with the next pair:
You see just those folds  runing back center leg to side seam and some up into crotch. It can be the trouser is not enough balanced. The back can maybe go up a little bit more. Pull up the back at centerback and look what happened. It is not much maybe 0.8 cm - I guess.
I attach 2 drawings from me which show the way even a poly cotton blend can be dressed.
It is essential that you move the iron the shown way when you stretch, the bias helps here to stretch. When you shrink (blue signs) you lay the pants in form and with your fingers push the surplus into little "waves" and steam that - the waves will shrink slightly. So the fabric will react a bit to that procedere (like Peterle wrote) - but not like a wool.
lg
posaune

[GipsyApprentice]

Many thanks for your reply and that great advice, I'll do it just like this in the next one, with a more "real" fabric though, maybe a wool blend, I've been using on cheaper fabrics just for training purposes, my real goal its to get a complete Rundschau suit quite well done...

You see just those folds  runing back center leg to side seam and some up into crotch. It can be the trouser is not enough balanced. The back can maybe go up a little bit more. Pull up the back at centerback and look what happened. It is not much maybe 0.8 cm - I guess.

In that case I suppose will have to shortened the centre back run up from the waist line level, in order to pull the back up as you say.
Again thanks so much for your comments and advices and for sharing your time and knowledge with us apprentices..!!!