Frontal Shots are not all that bad of a shot if you place it. I took one last year with open sights at 52 yards shooting a flintlock. I probably would have taken the shot. At 15-20 yards a neck shot would have been almost a give-me with open sights or a scope. When they had their head down, not looking at me, it would have been all over for them. Remember, break their neck, or penetrate the brisket and there is heart and lungs there that you can take out. Also if you were shooting an XTP with a reasonable charge, it would have penetrated, expanded, and did the damage.

BUT

Let me commend you for not taking the shot. From your question and your actions its apparent that YOU were not comfortable with the shot. And based on that fact you made the wise choice. You wait, hoped for the shot you wanted, and took your chances. You were not comfortable with what was presented and because of that you did not shoot. My hats off to you.