Bromide drag is the reason I am not doing this regularly as I got plenty of streaks even doing semi stand, but I might retry with having empty reel at the bottom. Because as you said, the edge sharpness increases lovely, making sharp slides to appear even more so! And flattens extreme contrast nicely.
How do you control contrast in stand? More developer?
If I could avoid Bromide drag with PQ Universal, I'd do both - Stand and SLIMT - employ one or the other where needed.
First, I would note that I process everything in the dark in 2 litre open tanks or larger. (I have temporary covers I place over the tank when I want to leave the darkroom between semistand or EMA agitations so I don't have to sit there in the dark for an hour!) This allows for plenty of developer and room to properly position film.
For sheet film, I use frameless pinch clip style hanger, though an X-Ray film clip would probably work. The idea is to hang the film horizontally so that the bottom edge is well off the bottom of the tank and to do this with the absolute minimum of contact with the film. Some people (Steve Sherman leaps to mind) have gotten very good results by making PVC tubes to hold their film to achieve this same idea...
For reels, I invert a small funnel, placing the nozzle in the center core of the reel. Then I feed the reel lift rod through the wide end of the funnel. That way, when I place it in the developer, the lift rod is there as usual, but the reel is suspended off the bottom of the tank 1-2 inches. As I mention in the paper I wrote, I'd avoid plastic reels and stick with the Nikor stainless type reels that have good spacing between wind layers.
To date, I have found this approach to work well with highly dilute D-23, DK-50, HC-110, and Pyrocat-HD. I initially prewet the film for 3 minutes in a running water bath temperature matched to the developer. I then continuously agitate the film in developer for 2 minutes and proceed with my agitation scheme thereafter (either semistand or EMA).
Image below is the sheet film hanger type I mentioned above.
With semistand, I find that explicit contrast control isn't as important as it is with conventional developer. For long SBRs,the highlights are controlled because of the compensation effect of not agitating very often. The shadows develop to completion because of the long standing time. For really huge SBRs, you can increase developer dilution. For example, my normal Pyrocat-HD dilution is 1.5:1:200 but if I have a highly contrasty scene, I will increase this to 1.5:1:250 or 300.
Short SBRs tend to have a lot of middle tone content. Here, the very long development time will expand that contrast considerably. For example, here is an image shot on an absolutely flat, gray day, with very little tonal range. Scan of split VC printed silver print:
Notice that the overall scene is a sort of low contrast gray, semistand has really made the midtones separate an 'pop'. Kachel has written a lot about the importance of midtone local contrast.
Another way to increase contrast is to switch from semistand and resort to more frequent agitations via EMA.
The hardest thing about this is getting away from the old Zone System of thinking about N+- development. With semistand, you're always reining in the highlights and developing the shadows to completion, so the extremes of N+-3 development just aren't needed. For this reason, I don't segregate film by SBR when semistand processing. Everything goes into the tank regardless of the SBR I was shooting at the time (unless I have a really extreme SBR problem to solve).
Note that there are times when I still develop conventionally. For example, if I want nice cloud edge effects, I develop in PMK Pyro agitating every 15 sec. If I am photographing people, I may resort to HC-110 or DK-50 at conventional dilutions and agitations because I don't want their faces to be razor sharp.
As far as bromide drag goes, I have seen almost no evidence that it is more- or less likely based on developer type. It appears to be more more an artifact of how the film is suspended and getting it off the bottom of the tank. I would not try this with a conventional daylight tank. Like I said, I use open tanks in the dark to give me room to get the film away from the bottom.
The one exception to this was very very old Plus-X (40+ years out of date) which consistently showed drag effects in Pyrocat-HD. Interestingly, it was just fine in D-23.