Why does my 'l' and 'ḷ' sound identical to natives?

I've been recording myself repeating words like 'pazham' (fruit) vs 'palam' (bridge) for weeks, but I still can't seem to nail the retroflex sound that makes these words distinct. I've been using Chickytutor.com to get feedback on my pronunciation, but even the AI keeps flagging my 'ḷ' as too dental. Are there any specific tongue-placement exercises for Malayalam retroflex consonants that actually work, or is this just something I'll never hear correctly as an English speaker?