Thank you for your detailed response AndreaColombo!
Now i think i see where my expirience become different from "common math" =).
First, i can't enchant Blade of the Endless Path with any lashes(its already have 11 points reserved, and i hope to apply legendary one - who's leave me with 13 of 14).
Second, and maybe its a bug, but Tidefall raw dot damage far more better in real fight than in tooltip. From one hit its do near 40 damage(main one was near 60) to target with two ticks(Interesting, but in combat log its only say it would be 20 for 4 seconds) and most of the time second one come simultaneosly with your next attack. So you on dumped INT max MIG character you can increase dot damage to be two times stronger than lash one! But if you increase your INT Dot damage become lesser, or maybe its more correct to say - normal, so i assume it's can be a bug( I think i saw a thread on this forum discussing this exact problem).