I'm pleased to report that I have tamed the plaid at the sleeve ... phew! I did it by the most plodding approach possible. If any one of you reading this has a better and more elegant method I would love to hear about it. In the hopes of giving those of you who are better at this than I am a good laugh I will now illustrate my half-witted approach. In its defence, it did work...
Once I had the jacket body assembled I went back to my muslin sleeve (for once, my muslin was actually cut in plain muslin fabric) and took it apart. I went back to the traced sleeve pattern which, as you may recall from this post has plaid matching lines on it as supplied by Burda. Using the sleeve cap matching line I placed the muslin sleeve cap piece on the plaid fabric. With a Sharpie marker and a ruler, I drew the main elements of the plaid fabric right on the muslin. I then basted the muslin sleeve into the jacket body.
What to do? At first I thought I'd just measure the difference by which the sleeve needed to be shifted on the plaid. You can see that the plaid on the sleeve is consistently lower than the plaid on the jacket body - it was about 1.5cm (5/8") off. Then I thought it might be a bit tricky to transfer my knowledge onto the flat fabric for cutting - does the pattern piece need to be shifted up or down?? It is a bit confusing, that, even with this photo to remind me.
My solution was dead simple. Once again out came the Sharpie which I used to mark where the lines should be, right onto the muslin sleeve, like so.
I drew marks at the main horizontal elements, but also the vertical ones on the cap. I've tagged one of these lines "Red" so I would remember which part of the dark plaid box it was.
The resulting sleeve, once set in, is pretty good, although not perfect at the vertical elements. I've read Kathleen Fasanella's posts on sleeve cap ease (she says it's bogus and uses a perfectly matched cap to illustrate - see part 1 and part 2). She says horizontal matching is impossible with sleeve cap ease, but I had no problem with the horizontal matching even though my sleeve pattern does have ease built in.
However, I'm still puzzling over how the tailors make a vertical line travel from the shoulder and directly down the front of the sleeve. In addition to the amazingly-matched sleeve cap in Kathleen's first sleeve cap ease post, check out the striped jacket in the first picture on this post from Made by Hand - the great Sartorial Debate - his right sleeve cap is flawless; the left one appears less so but I suspect this is only because of the angle of the photograph.
Maybe some day I will be able to manage this but for now, I have to settle with "good enough". Pictures will follow once I have the jacket a little further along.