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What about setting a min-max range for the Tx fee? Minimum, say in terms of the minimum YAC unit, 0.000001YAC (or 0.00001CENT), a Satoshi or whatever we choose to call that minimum, say 100 Satoshis. And some maximum, or a percentage of the Tx amount, of TX byte count size or whatever, whichever is smaller. Doesn't seem hard to do.
Tx fee's function is to prevent blockchain bloat/spam attacks. Lowering it would mean removing this protection.
The only way it seems sensible to have it dynamic (and less than 0.01) is to somehow tie it to block reward.
More miners, consequently higher difficulty and lower reward would indicate possible higher price. In that case it would make sense to lower mandatory tx fee.
As it is now, at such low price, tx fee could even be 0.1 yac.
I admit it is challenging to estimate price from difficulty, especially considering N factor.
Besides, I think tx fee is perhaps even more an economical than security issue. And we've got enough of those to fix.