Are you considering a transplant or something? If you got your hairline filled up, but continued to lose diffusely, you could end up with just the tp hairs in front and much less behind them. Could need lots more work over the years to fix it up.
If you are considering a tp, I'd go with thickening just behind the hairline and throughout the top evenly.
Not sure what treatments you've tried. I've been fighting recession/diffuse loss for years. Using minoxidil over the last year+ I've regrown moderate hairline hair and had good thickening everywhere else.
The hairline is still thin and diffuse, but the thickening of all hairs around it makes it look far better than it had.