As for stifftie, you can "set" it at age 2 but it should have no effect till the tie stiffens. It is a value that stays put forever so this is OK.
I don't think fixlen works that way tho. I think if you set it too early it doesn't do anything.
Well, there's one bug in 2.4 then. The current code zeros out .stifftie, .fixlen and sets .fixang to 32000 the cycle after a value gets placed into tienum.
So, is .tienum the actual trigger then? The 2.4 code may be backwards and treats these others are the triggers. Currently, any value placed into tienum persists across cycles (there is a line to set it to 0 at the end of the cycle after all the tie operations have happened, but it is commented out).
Also, I have been playing with Helios using the fixed radius mode in 2.4, which should eliminate the different bot size issues. There are still issues. It forms pairs, not quads. I think the tie physics are what is changing the realtive positions and failing the quad formation as well as possible sysvar issues. Will keep digging.