Ever since I've owned a Suzo Home Arcade joystick (from my Atari 2600 until now) I've loved leaf switches. The really early one's had leafs, later stupidly, Suzo changed to MS. Anyway, I think you could have two (or one of them) problems:
Take a look at the drawing I attached. I had always seen how some arcade buttons were so very much higher sticking "out" of the button rim than others. It was only until I restored my Galaxian CP that I discovered what caused this. ( I prefer the lower setting).
If you look at the drawing (this is from the Galaxian manual) then you see that the button is kept "in/downwards" by rings Number 4.
If you leave these rings out, the button is much higher, and you need to press it down a longer way.The rings are giving you a "head-start" by keeping the button closer to the upper leaf.
The other thing: take note of the amount of space between the CP and the leaf switch. If the lower leaf is too close, you will be bending it down (unnecessarily) deep. The principle is, that the upper leaf just touches the lower one when the button is pressed ALMOST completely.
At least, that's the way I like it.
That's one of the extra advantages of leafs over microswitches: you can set them up the way YOU prefer them to be. Like tuning a race car. Tune it wrongly, and the car will feel lousy...same thing with the leafs....
About springs: I ordered 3 new white buttons for my Galaxian from Arcadeshop.com. Two of the buttons were exactly alike, but the third was just a bit different. One of the things was that the spring was a LOT tenser then the other two. So much so, that I decided to replace that one with one of the ancient springs that were still in the old buttons of my Galaxian (of course, I took it of the 2 player button, least used !)
I like my springs to be "weak", I don't like to use force to press a button...I can imagine that a tense spring is tiring more than a weak one...