My bitch had this issue... she had soft ears. Your window is closing, but that's about the age (I think) I got desperate after trying foam inserts, taping, etc. and used tear mender glue and a cone to keep her from messing with it. It did work, and her ears finally both stood. I don't remember if it was her tattoo'd ear or not... but maybe it was. Seems that the heavier boned plush and long coat dogs are more likely to have the soft, floppy ears. I'd try the glue and cone, but you need to do it very soon. I think it was a week or two that I left them glued. Also, if your dog will chew, give the dog as many hard things to chew on as possible.
Wrath of Grim z Dragon
"Mr. Grim"- Threaten my handler. I dare you.