Fitting trouser muslin

[Bifurcator]

I'm not expert and a learner myself, but visually...I'm seeing the same thing Posaune is seeing with tightness at the hip, I think you could use a little ease there.  On the front you can see, what appears to be stress wrinkles radiating horizontally.  This may also be due to fabric wrinkling, which looks like it could use a good pressing

It seems like your back rise needs some length, as it appears to be diving in a little and the fabric around the upper thigh also looks like it's being pulled forward.  I think this is what Posaune was referring to with cutting out the back crotch, which I think is also called "scooping", but could be wrong about that. This will give you're body a little more room there and lengthen the seam. I'm curious what straightening the back crotch seam will do to the fit.  My knowledge/understanding is still lacking in that shape and area tbh.

[Bifurcator]

also for your fly stitching you mentioned some troubles sewing...
I find stitching the J stitch from the bottom up is more forgiving as any excess can be trimmed from the top.  It does look like the fabric is being stretched when sewing at the fly front so maybe just slowing down, controlling/moving the fabric under the needle so the feed dogs aren't pulling the bottom while the presser foot is strethcing the top will help.

[DrLang]

The J is actually hand stitched. I like the look of it with a half back stitch. It has a subtle appearance. Also bottom to top. Some of the problem there might just be the cut. I am thinking maybe a similar issue as with the back crotch.

I have adjusted the back seam a bit and Posaune was spot on with the issue. It's not perfect, but it is substantially improved. Of course, major adjustments there means that I need to add more at the side, and I was just not able to squeeze much of an inlay out of the fabric that I used. Not to mention that corduroy does not play well with being let out after a seam has been hard pressed open. So opportunity to fix this piece in particular are limited. I have one other thing that I want to try before I take some new photos. The local tailor that did the hem on my last pair wanted me to send photos of the next, so I feel obligated to do the best that I possibly can now before I do that.

The wrinkles on this are tough. What you see is almost as well pressed as I can get it. The angle of the light with these photos gives about the worst possible highlighting of the wrinkles. Good for seeing drape problems, but terrible for stubborn wrinkles on cotton fabric. I would just there to be about 4" of ease in the hips just below the pockets. It seems there is almost none at pocket level. So yeah... I think some cotton chinos might be in order for the next pair just so that I will have something easier to adjust and assess changes to my pattern.

I was hoping to cut trousers from my suiting next, but I think at least one more go at it is in order. Unfortunately, winter is also going to wrap up soon, which means I will be busy with other stuff. Progress is going to slow way down for a while.

[Bifurcator]

oh wow- hand stitched J stitch- nice.  It may just be the photo or corduroy fabric to be fair and as you mentioned the light/reflection.  I recently made a cord pant and struggled with the unevenness of the fabric especially with edgestitching and smaller details. Maybe, partly why corduroy is a more casual fabric.