past conditional

it would be better if you knew exactly
it would have been better if you knew exactly

how can write this in russian

было бы лучше если бы вы знали

in both case ?

I have a little problem with English here, otherwise both sentences are translated the same way into Russian, i.e. the way you did.

unless you are talking to a friend and then

было бы лучше, если бы ты знал

but i'm sure you know that

Well the first one takes place in "now-time" and the second in "past-time"

It would be better if you just said what is on your mind... (someone has a hard time saying something straight)

было бы лучше если ты прямо скажешь(/говоришь?), что на уме

It would have been better if you had studied before the final.
было бы лучше если ты учился бы перед тестом

Right?

1. If the second one takes place in the past, my understanding is that tenses have to match (or is the rule outdated already?)

it would have been better if you had known exactly

Regardless

2. было бы лучше, если ты прямо скажешь, что у тебя на уме

"takes place" in the future, the immediate future possibly, but in the future nevertheless

Было бы лучше, если бы ты прямо сказал, что у тебя на уме

can "take place" right now or in the past (see 3). If it is now, the meaning is virtually no different from the sentence above, maybe it is less assertive.

3. The "now time" and the "past time" conditionals are no different in Russian

Было бы лучше, если бы ты знал это сейчас
Было бы лучше, если бы ты знал это два дня назад

are both fine. The reason for that is the nonexistent perfect tenses in Russian.

"It would have been better if you had known"