I made my daughter this cardigan and it got felted in the wash. 
I said I would make it again for her and she said that the sweater was perfect except that the upper arms were pretty snug. For any of you helpful people who have not made this one, the cardigan is knitted top down and the sleeves are made with German short rows in the cap area. I asked on Ravelry about this problem and the moderator (not the creator) of the patten suggested I just lower the armholes (by adding a few more rows on the front and back at this point in the pattern. Hmmmm. It’s been my experience (from sewing) that lowering the armholes restricts arm rotation. Also the sleeves have a number of decreases from the armhole to the cuff… I’m wondering what you think the best options are?
Let me add here: my daughter’s bicep circumference is 39cm and the pattern bicep circumference is 35cm. So, I don’t think it would take much.
Funny enough, I was looking for something else today but ended up reading about lengthening an armhole to increase size in upper arm or chest. So perhaps the moderator was not so wrong?
I would start with the 39cm add some ease, and then work out in your own gauge (if it differs even very slightly from the pattern gauge) how many stitches are needed in the upper arm (not cap) to get the measurement needed. Then look at the pattern and see which size is closest to that stitch count. See how big the armhole is for that size, how big the cap will be and so on.
If the sleeve needs to narrow more than the larger size you can recalculate the decreases to get a nice snug cuff.
I have always been bigger in the upper arm, although I’m not big, but shop bought cardigans never fitted well on the arm and a size bigger would look too big in the body. I should have knitted my own!
I really don’t have experience sewing like you and others here do, I am useless at sewing, really not my skill set. But perhaps the slightly bigger armhole works in knitting when it wouldn’t in fabric because the knitted fabric has give and stretch in it?
Thank you, @Creations. Funny, I was thinking similarly about looking at larger sizes when I got to the sleeves, Initially, I thought of just adding cable CO at the armhole and increasing the number of stitches in the wrap and turns but I don’t think the construction includes those… It’s going to take some thinking about. 
And, yes, my daughter’s bicep circumference is small but muscular. I have the fitting problem of broad shoulders and narrow hips so most of my early outfits were blouse and skirts. 
Oh, my bad. It IS constructed with cable CO at the bottom of the armhole. That may be the solution. 
It seems to me that you may need a combination of the slightly longer and then casting on several more sts for the sleeves when you get to them. It won’t take more than 2 rows or so increasing depth to the armhole and a several more sts to the sleeve to fill in the extra depth.
Great looking pattern from a wonderful designer!
Thank you, @salmonmac! My only issue with adding rows is that (I believe) it would have to be 4 rows because of those faux cables running down the front. I struggled with those the first go around because if I was off by anything, even a row, those were a nightmare to keep track of on both sides as I knitted down. Maybe just add the cable CO… and pray. Or would short rows work at the lower area of the armhole? I adore Kraemer’s patterns but they do stretch my brain. 
What is your row gauge? I think adding 4 rows might be plenty…at the gauge given that would be about 1.5cm. Yes, in sewing, lowering the armscye can restrict movement, but knitted fabric is stretchy enough that it shouldn’t be an issue. Even in fabric, 1.5cm shouldn’t be significant (speaking from 40 years of drafting patterns for theatrical costumes).
I was going to suggest that you could compare the length of the shoulder to underarm on the size you’re making and the next size up, to gauge how much to add, but I just noticed that the next size up is SHORTER there? I still think you could safely add 4 rows (and add them to the sleeve cap as well!), to get a lower armscye, and then maybe use the directions for the larger sleeve.
This is such a pretty cardi! I’ve added it to my Favorites. Are the sleeves sewn in, or picked up and knit on? The armscye detailing is quite attractive, and I do love a set-in sleeve!
Yes, I’m sure that keeping track of the cables is busy enough. Ah, yes, the cables at the sides. I think you could do 4 rows at the row gauge given for the pattern or close to it (26rows/4inches).
Thank you both @ColoCro and @salmonmac! And especially for the reassurance that a knitted garment will be different than a sewn garment when lowering the armscye. New word for me. Thank you for that as well. I think I will do this, just adds one more of the faux cables and at 1.5 cm it should do the trick. And my gauge is exactly that of the pattern. The sleeves are picked up and knitted top down, BTW. Love, love, love this pattern and the way it looks and fits. All her patterns are incredibly detailed and knit up beautifully.