Another factor that is very relevant in open sights is your Sight Radius. Your sight radius is the distance form your rear sight to the front sight. The large the sight distance the more accurate they are. So a hunting rifle with both sights on the barrel 20" apart is not going to be as accurate as a rifle with the sights set at the rear of the receiver with a sight radius at 25".
Also the distance from your eye to the rear sight will affect your sight picture as well.
It should be noted that the distance from the shooter's eye to the sight combination (dependant on the shooter's stature and stance) is an important consideration:
For a shooter who holds the pistol closer to the eye (smaller stature and/or bent arm), the rear sight gap will appear wider in relation to the front sight blade
For a shooter who holds the pistol closer to the eye, the front sight will appear wider in relation to the target.
Due to the effects of perspective, the rear sight gap will APPEAR wider in relation to the front blade – e.g. for a front sight blade width and rear sight gap both of 3mm, the APPARENT sight ratio for most shooters:
with a sight radius of 200mm will be around 1.25:1
with a sight radius of 150mm will be around 1.1:1
That is from Sight Radius - Shooting Wiki