The filter AS IN THE PHOTO looks fine to me. If you added another cover sponge then the motor would be under extra load so that may wear the motor out faster. I don't think you need any extra cover, as per the photo is enough and I doubt the filter killed the shrimp, I expect the shrimp died and then got sucked onto the filter? Also if you added a finer sponge it will block quicker, both sponges should be rinsed in tank water weekly, the same if used as per the photo. I very much doubt the suction from the filter would be enough to catch a live shrimp and kill it?
If you do get a new filter you should just leave the sponge from this older one in the tank for a few weeks as it is covered with bacteria!
My tanks are similar size to yours and I use these types, 2 per tank (with the spraybar attachment), available everywhere in the world (many different makers), cheap and super easy to use,
https://www.pro-shrimp.co.uk/internal-filters/1826-superfish-aqua-flow-50-8715897041747.html
On the very base is a cover, I remove that so there is extra sponge surface, and then to clean the sponge you just rotate the whole unit 120 degrees on the glass and pull the sponge out! Soooo easy and quick!
These are the most popular with shrimp tanks, with an air line,
https://www.pro-shrimp.co.uk/internal-filters/1486-superfish-double-sponge-filter-xl-8715897249938.html
Having said that, what you have looks fine AS IN THE PHOTO (unaltered) and I would just carry on with that if it still works, but squeeze the sponge in tank water weekly to clean it!
The bacter AE sounds ok, but I would use that just twice a week!
Simon