For me, its all about positioning. If he is lying down on his back and I am over him, I can position my head and take him all the way to the balls (he's a solid 7.5) repeatedly. But if Im on my knees and he is in front of me, I can only do it for a couple strokes and then I need a break for a sec. His favorite thing is when I "swallow" with him in my throat.
Sometimes I can and sometimes I can't. I guess it is just like anything in life. You have your good days and your bad days. Would love some tips if anyone has them! Hubby loves it when I can manage it, but I wold like to be able to do it more consistently.