Hi Mike, more expert practicioners have already posted here than me. But I have done quite a lot of split toning with Selenium, hopefully I can be a little help.
As has been mentioned, results can vary a great deal given (apparantly) the same conditions and materials.
But most sig factors seem to be the usual; Materials (paper in particular and dilutions), temp and time.
A warm tone paper like Multigrade will enhance the brown/sepia, whilst a cold tone allows greater action by the Selenium enhancing the DMax, with the warm sepia appearing more subtly.
I've had great results on Agfa MC111 with a full range of results available using Sel and Veridon. This gives a different result to Roman L's work, who definately uses Sel + Sepia, and I suspect Gold also. But the process is the same.
My process goes:
1. Make sure Stop bath dilutions are correct and fresh. This seems to be a cause of uneven toning, if not right.
2. Also, make sure print is fully washed (archival if possible) after fixing. I wash for 60mins in archival washer at this point.
3. Tone with Selenium until DMax deepens. I generally use 1:6 for about 2 mins on MC111. But the dilution and timing will vary with the paper and content of your image.
As the Selenium toning affect is more subtle, I like to Sel tone first and use a wet reference print beside the toning tray, in daylight. Check it frequently, it is important to preempt the colour change. At this point, not all hallides are converted leaving room for the Sepia action.
4. Arrest the action by washing thoroughly again. I give it another 30mins in archival washer.
5. Now tone in the Veridon (or Sepia) to completion. Depending upon the amount of prior action of the Selenium and the receptiveness of the paper, you will see a subtle rich sepia or brown through to more pronounced two tone sepia or brown.
6. Archival wash.
A good way to get control is to have 1/2 doz prints all printed the same time and the same way, and then changed the length of Sel toning for each.
Lastly ...... throw lots of paper at it

. Don't be disheartened by the inconsistancy. Last year I had a print in a show that had toning just how I wanted it. Because of this and the schedule, I had sent it through with a minor defect (hoping that just for the show, it would be missed). I was asked to reprint it, but never been able to reproduce exactly the same tone.
Can be frustrating, but that's the fun of it too!
best, John