But other options like a "factor" etc. makes easy changing of some jail separatelly, for example without changing a master multipliers or other default values. For example, I can set "maxtime" bei mail-jail to 1 week, and leave it for ssh-jail by 2 hours (if I use a certificate it is enough). I would like to be just flexible.

Oh, by the way: the proposal of @yarikoptic (multipliers) has already been implemented in this branch. And even with "permanent" ban, for example the configuration below will increase a ban time up to 2 years:

bantimeextra.enabled = true
bantimeextra.maxtime = 2*365*24*60*60
bantimeextra.multipliers = 1, 2, 4, 8, 16, 32, 200000

But of course, I can also map the value -1 to 0x7fffffff or something near it, without great changes in code.

But as I already say, the problem at the moment makes findtime+maxretry...