what plants.. how about a pic ...

You shouldn’t wait until the leaves are telling you. The plant is already in drought response by the point and that’s needlessly stressing the plant each time.

There is a lot of information/suggestions on Youtube that suggest what is referred to as "the taco test" meaning that you can bend the leaves into a "taco" shape as an indication of when a hoya needs to be watered. I don't subscribe to this method. If it works for you, I'm not going to try to talk someone out of it.

But there are literally thousands of varieties of hoyas. Some have soft leaves by nature (think of australis). Some have very rigid, thick, succulent leaves that don't bend easily. Some have needle-like leaves (linearis, retusa). Some have tiny leaves no larger than your finger tip. Do you really want to bend those leaves all the time to see if it needs water? No. I don't.

I treat most of my hoyas the same way. When I water, I water full, all the way through. Then I let the water drip from the pot until it stops dripping. Then I put it back on its tray and it goes back in its home. Then I don't water again until the pot is almost completely dry. Sometimes it goes all the way dry. I can tell by the weight of the pot, sticking a finger or skewer into the pot, or I do sometimes gently squeeze the pot and if it makes a crispy sound, it's dry. This is usually 10-14 days. I try not to let it stay dry for too many days (although sometimes I forget to check. I'm not perfect.)

I do have a few exceptions to this. A couple of hoyas in very large pots. I water those differently but they are never completely dry. And I have some hoyas in semi-hydro / leca.

I don't know for sure, but I suspect your roots are getting too dry for too long. Maybe the media is sucking the water out of them too. Then when you do water, it's too late and they can't take up the water which causes them to dry out further.

I hope this helps! The good news is that you can pretty easily re-root hoyas. They are rarely a total loss.