I seem to be very light according to your estimate as I am at a 1/4" being my high end.
When I first started making calls, I had a tendency to stretch the material with less tension than I typically do now. In the end, it is all about finding the right combination of tension in relation to the thickness of the material you are using,...and also as it relates to all the other factors involved.
For example, I started out using mostly .003 material and proph for most of my calls, and I probably put something in the neighborhood of 1/4" stretch in them. More recently, I use mostly combinations of .004 material as the primary (top) reed and with .003 as the back-up reed material. For me to achieve the pitch and tonal qualities I am looking for, I have to stretch that heavier material more tightly than the thinner stuff.
Again, there are many factors that come into play in mouth calls that impact sound. Hitting on the right combination of reed materials, layering, reed spacing, stretch (including side, back, and even front tension), and cuts often requires a great deal of experimentation,...and a bit of good luck, as well. There as literally endless combinations of all of those factors in making calls.
Finally, at the risk of sounding like a broken record, understanding how the reed cuts impact sound and knowing how to adjust your reed cuts to get each call to where you want it to be is the single most important thing you can learn to do,...in my opinion.
Fortunately, mouth calls are pretty inexpensive to make,...and for me at least, making them is an enjoyable way to pass the time between seasons.