Self-recording my pronunciation: Am I overthinking the 'hỏi' and 'ngã' tones?

I record myself daily and listen back, but I feel like I'm hitting a wall with the 'ngã' (~) tone. It often sounds indistinguishable from my 'hỏi' (̉) tone to my own ears. Aside from just repeating the same words, what specific tongue or throat positioning should I be looking for to stop the 'hỏi'/'ngã' merger in my speech? I am asking specifically about learning Vietnamese, not a generic study routine.