How can I use cftool or any other function to get a fit for an oscillating function bounded by an upper and lower envelope function?

I am trying to curve fit a data set that resembles an wave bounded by and upper and lower function using cftool. However all my attempts either don't converge or come up with poor fits.

I have tried a simple case where my data is defined as y = (1/x^0.5)*sin(x). In cftool i use a custom function fit and input the form y = (a/x^b)*sin(cx+d). Despite having almost the exact form of the data im trying to fit, cftool converges on a fit that is still a poor fit. Aside from leaving providing the function form, i have left all the other parameters at their default settings. Is there a way I can adapt cftool to make it more adept at fitting oscillating functions bounded by an upper and lower envelope. In my actual data the upper and lower envelope are different functions.

Thanks