A tall reactor will work just fine, and might actually be preferred over a big foot print and short height.
I used to run mine in plastic 55 gallon drums. I had small holes in the top to get media and parts into the drum, that sucked to deal with so I cut the tops off making them open topped. Then I added prazi one night before bed, checked on it in the morning and half the media was on the floor. Back to the drawing board.....
Prazi means under heavy aeration you'll make foam, the K1 will float on this and not only dry out but actually spill out of the container. Now a simple screen could prevent this, but it will still dry out. Now if you were to add a drip tray above the water level with water running over it then there's no way for media to dry out.
Bio reactors are designed to be used like a UV. They are supposed to be low flow, high contact time, so best to run them with an auxillary smaller pump in another loop off the sump. So if using on a central system could just drop a little 1-2K gph pump into the sump next to the return pumps and run already mechanically filtered water to the reactor then dump back into the sump. Several people have proven that reactors work fine with higher turnover as well, but the original intent was slower flow rates. IF you do use basically in the main sump you can benefit from taking the thousands of gallons per hour of turnover in a central system and drive all that through the reactor and get a really good boil, but all this turbulence will take the dead bio with it, so it's best to filter AFTER the reactor as well. I filled up a pot scrubbie wet/dry with dead reactor bio by feeding the tower with the reactor, and the scrubbies just kept all the crap in them.
IF you do add to a central system you will need to start removing the bio balls to get the K1 to seed right. I had to loose a lot of media before the reactors really seeded.
Also worth mentioning, the stuff doesn't boil right new. Might be best to media bag it and let marinate for a week in the sump before sticking it in a reactor and trying to get a nice boil.
I'll post some pics later tonight of mine so you can get an idea of how to deal with the strainers being a pain. The surface area of the strainer has to be huge or the suction will pull all the media to it and slow the draining.......