If you like red colored dissectum，red dragon is my favorite. It is slow growing and never gets too big. Mine has been in ground for 5 years now, never with winter protection, it has been doing great and no die back at all. It is one of the very few trees that retains the beautiful red color even with most shade locations.

Another one I like very much is Shu Shidare. Also never gets too big, winter hardy, easy to grow, the color is ever changing. I have it in container and in winter i bury the pot in ground without any winter protection. Spring has the beautiful orange then other color mixed in throughout ghe growing season. Fall is orange red. Mine seems to be upright and weeping so fit your location well.

Looks to me like there is a lot of green already there. I would go with either a Fireglow (smaller size) or Hefners Red (Larger Size) red leafed maple. If you want to stay green I would put Summer Gold, Jordan or Orange Dream (depending on amount of shade) there. These would add some color pop there, I would check the hardiness ratings for your area on them though.

I agree 'David' I do think a red will make that corner pop.

(Just throwing it out there but what about a "Carnival"?)

Sorry, after rereading your post I saw the size requirements, with that in mind I still say Fireglow along with Purple Ghost and Amagi Shaguri (sp) for reds. Aradien, Koto No-Ito and Akane for something different. Also there's another I'll add when I get back home.

The other one I was thinking of was Okukuji Nishiki.

I still would consider Hefners Red, Orange Dream & Summer Gold as I think In your zone they might be slower growing than in mine.

I think you need more height and less width in that corner than a dissectum would offer. But not too much height, as that would shade out the surrounding plants. I'd consider 'Shaina' as a good possibility.

'Villa Taranto' is anther possibility....never gets too large, goes through a series of appealing color changes (including red) and has very narrow, finely lobed leaves that somewhat give the appearance of a dissectum but without the weeping habit.

To be honest, there are a good many choices to select from :-) Might be best to check with local suppliers to see what they offer, as you will get a much larger, more mature tree that should be suitable for your location than you would if mail ordered.

I think you need more height and less width in that corner than a dissectum would offer.

I agree.

than you would if mail ordered.

(I would never have mail ordered).

"(I would never have mail ordered)."

LOL!! Neither would I!! But apparently a great many JM growers DO order their trees by mail. I guess if local availability is lacking or they are collectors, mail order does make sense. Fortunately, I live where there are great JM sources (my nursery buyer can bring in any cultivar I want if given sufficient notice) and I really need to see my trees before purchasing.....so it is not an option for me.

UPDATE (July 2019):

Of course I know you were all waiting for the decision ;).

Too make a long story short, late last Fall I reluctantly moved a previously planted EDNA BERGMAN JM to that back corner. It came through the winter perfectly and has been so vigorous this season.