It’s 160% stackable attack max for Tarlak’s buff.
Yes, the HP condition has to be met for the Ranvir buff to apply. That’s still 160% attack maximum, as opposed to 195% with just Ranvir’s buff.
Tarlak + Ranvir is difficult to manage and set up, not effective nor worth it when there’s better options available.
You generally don’t pick and choose who the enemy hits, making it unpredictable to prepare for when your HP will be lower. It’s even more difficult to manage those skills together because Tarlak also casts a passive HP recovery which would eventually bring your HP higher than the enemy.
You’re better off using Tarlak + Boldtusk, which gives a 148% attack buff at all times, it’s not 160% but it’s very close. If you’re fortunate enough to have both, Tarlak + Khiona can bring her and two other heroes to 145% attack + one more hit caps it at 160% already, which again is active at all times and is much more reliable to set up.
Not to mention it’s better to combo Ranvir with those two heroes as well… with Boldtusk you get a 48% attack buff at all times but a massive 243% buff with a -35% accuracy penalty when enemy HP is higher, because there’s no attack cap there.