I see, but in your case I'd have to draw their faces infront of the speech, just to show whom the phrases belong to. It is quite a bad idea, as the whole pic is really small, the characters' faces would ruin the 'shot' feeling.
But, you're right. Definitely some details are covered with text.
Nice Iso, but I would put the text below the picture, like a subtitle. It's hiding some good detail.
Even though I'm not a fan of the series, this looks awesome, detailed and funny!