The revised muslin

I'm sure I can get this shirt to fit better.  I'll start with some easy fixes and hope it will be enough. 

I'm not a fitting expert.  These are just a couple of techniques that have worked for me in the past.   

Fix #1 is the easiest -- adding some shape to the back.   I start by laying a piece of Swedish tracing paper over the pattern.  As you can see the top of the back on the pattern is completely straight where it attaches to the yoke.  Therefore, there is no shaping to the back.  The shirt will fit better if the back seam is curved.  Starting at the shoulder seam I've drawn an arc up to a point 1.5" above the existing pattern.  That's it.  The curved back sewn to the straight yoke will act like two horizontal darts pointing to the center of the back.  You may also notice that the pattern as drawn has 7 small tucks across the back.  Personally I think that's more woman's blouse than man's shirt, so I'm going to fashion the excess fabric into a center box pleat.  

Now I move to the front for fix #2 -- the sloped shoulder adjustment. The pattern as drafted would only fit me through the shoulders if I inserted HUGE shoulder pads.  So I need to increase the slope of the shoulder seam.  It's a two step process.  The neck opening and front edge of the shirt will stay the same.  I drop the sleeve edge of the shoulder seam down 2" and redraw the cutting line from the original neck line.  Above you will see my new pattern laying over the original.  

On to step 2. 

Now I slide the pattern up until the new shoulder / sleeve point meets the original armscye.  The armscye is then retraced.  This process raises the center front of the shirt somewhat, so it may be necessary to drop the neckline just a touch.  I'm OK with it, so I'll leave it alone.  But if I did want to make that adjustment it would be very small, no more than 1/4".  

Here's what these adjustments have done after pulling the shirt apart and roughly basting it back together. The shirt now fits better across my upper chest, and the huge diagonal folds are gone. Yay! 

The back now has some shape across the shoulders.  I've also tapered the side seams and taken 4" out of the shirt's circumference.  Is it perfect?  No.  Is it better?  Hugely!  I'm satisfied with the improvements,  so I'm moving on and cutting this baby out.