Can you post a picture of the window frame?

Is the headrail wood? Can't tell from pic. If it is, just drill right thru it and skip the L brackets. Normally L brackets are used at the sides or bottom, not the top. Not sure they were meant to go on like that to begin with.

Here’s the frame

The head rail looks like there’s MDF under the fabric cover

These instructions definitely call for the L bracket but I think it’s in part for versatility since they ship the same brackets to ppl doing outside mounts as well

I'd take the bracket to a hardware store and look for shorter one that will work with your windows.

Mount them as needed. Then add another layer…for instance a faux Roman Shade.

Rod mounted higher and wider than the window, this design will solve your problem.

https://www.etsy.com/listing/243233228/faux-fake-flat-roman-shade-valance-your?gpla=1&gao=1&&utm_source=google&utm_medium=cpc&utm_campaign=shopping_us_ts1-b-home_and_living-curtains_and_window_treatments-other&utm_custom1=k_CjwKCAiAn7L-BRBbEiwAl9UtkMXfO5aEhE53XKObANLNXmx8QcwZjOcjMYXunch1Dtb4_NkaaXxn2RoC04UQAvD_BwE_k&utm_content=go_1844177666_69409540523_346428665693_pla-304649336784_c__243233228_117913388&utm_custom2=1844177666&gclid=CjwKCAiAn7L-BRBbEiwAl9UtkMXfO5aEhE53XKObANLNXmx8QcwZjOcjMYXunch1Dtb4_NkaaXxn2RoC04UQAvD_BwE

You can do an inside mount without the bracket. Get long wood screws and large washers and screw up, into the window header.