So I installed a Dawson Precision fiber optic front sight on my 226 today. Followed the instructions about filing the front edge of the base. No problem.

There is a gap under the base of the sight and the base (flat part) of the dovetail slot. I can live with it if normal.

Additionally, the looking at the front, I can see a bit the sight base visible above the dovetail. Seems more of an aesthetic issue but would like to black it out. Any suggestions?

Never had a problem installing mine. I did however take materiel off of both the front and rear edge of the sight until it fit in the dovetail. If I remember correctly I did measure the depth of the dovetail on the gun itself and took of just ever so slight of a bit of the bottom of the sight base leaving it about .003 to .005 inches taller than my depth measurement before fitting into the dovetail slot. Ended up with a perfect fit and as good as any factory installation. (word of caution, be extremely careful and do not remove much of the base. Better to leave the base alone than take much of. You can fit it with the base being slightly higher than the dovetail cut.

I ended removing it, filed a bit more off the front and reinstalled using the supplied tool rather than the sig sight tool, fits better but still a bit wonky in that I can see some of the base above the dovetail on the front.

I might buy another one and try again.