Adjustable plates allow for additional negative camber and positive caster. I got my first set from Ground Control in California. They were actually E30 plates, but they fit just fine. I cut a little off the corners to allow a little more adjustment in the relatively small E28 strut tower.
At first I had a small problem, but Jay Morris at GC was dedicated to ensuring my satisfaction. A design change fixed the problem I had so now I can honestly recommend them. The only problem remaining is the small adjustment allowed. This is due to the geometry of the strut tower and is not a problem with the GC plates. If you ever consider camber plates or coil-overs for your BMW, go to Ground Control first.
I now have a set of over-the-strut-tower plates in my car and have several track days and autocrosses on them. I have even taken measurements for possible E30 applications. The E30 stut tower has an identical bolt pattern and even more underhood clearance. The E30 would still require a different strut brace, though.
I used a HUGE teflon lined spherical bearing assembly from a camberplate for another car and made two pairs of custom plates to fit my E28.
I can no longer use my standard strut tower brace because the camber plates now reside where the brace was. I had to drill the three bolt holes oversize to fit the three high strength socket head cap screws. The hood also needed to be modified to fit. At first, I was afraid I'd have to punch holes completely through the hood. I was planning on using the strut tower bulges from a Mitsubishi 3000 to cover the holes. It turned out all I had to do was remove some of the stiffening ribs from the hood. I'll have a new strut brace designed and machined before the first track day this year.