Work = √( time * weight ^ 2 )

I have observed that each time I increase the weight on an exercise, my calculated amount of Work decreases. I think this points to that the concept of work and how I measure it is not describing reality so good. It's not likely the case, that I happen to be weaker each time I increase the weight, but otherwise continue to get stronger when I only manage to lift the same weight for a longer period of time.
So basically what this implies, is that the weight used matters much more than the time it is lifted. They are not both linearly related to the Work output. In other words, if you increase the weight by 50%, you are not just going to see a 50% decrease in time under load, but rather an even bigger decrease!
So I changed my Work formula in hope of it describing my advances more realisticly. Since weight matters more, the formula should look like
W = √(time * weight x) 
In words, this is the square root of weight to the power of x, multiplied by time under load.
Now, x is some exponent that descibes how much weight matters when it comes to the work performed.
Now, in physics work would be measured by force times distance of course. But I use time instead since it does require work to even hold the weight in statically. And I'm doing super slow movements, so this should be ok I think.
Anyway, right now I've decided to set x to 2. Why? Because it gives the same increase in Work as if I just follow the curve from increases in time (when weight has not increased). So basically I'm saying that I should be able to increase the Work output at the same rate, even if I increase the weight used (and the time under load will of course decrease).

I have no idea if I'm looking at this the right way... any comments appreciated!