I presume your "longest bet run" means longest sequence of consecutive loses. If so, I am a little bit concerned that out of all your attempts, your longest bet run is either 27 or 28. Seems a bit strange that regardless of balance at any point in time, it should remain more or less static.
Not sure if I got the question right.
The "longest bet run" is indeed the longest losing streak.
It is not a fixed number because of rounding issues, I guess.
It is almost a fixed number, because I adjusted betsize to Max(Initial Betsize, Initial Betsize * Balance).
Think of it that way:
Balance = 10, smallest possible balance = 1, halfes every loss:
Balance = 10,
Balance = 5,
Balance = 2.5,
Balance = 1.5,
Loss
The longest possible losing streak in this case is guaranteed less than 5. My bet scheme behaves in the same way, because of the betsize adjustment. To be honest, I realized this "fact" the first time after reading your post.