I've dedicated a good portion of my career in gunmaking to building competitive shooting rifles/pistols.
It's been my experience that 99.9% of the better trigger pullers (like Mid Tompkins, Nancy, David Karcher, Tubb, etc) don't want stray ambient light on the front globe. (which is the whole point of a globe, to tone down the direct light on the front aperture/post, etc) The reason is the glare will create a number of problems. Elevation, windage, eye fatigue, etc. . . This would be why many NRA service rifle guys can't wait to Leg out and move into a Match rifle. Sights are sooooo much easier to work with.
Generally when the front Iris is hard to distinguish you either open the rear aperture or increase the width of the post, Iris size, etc. Color filters can sometimes help. (yellow or orange is often a popular choice)
Sights (metallic) need to evolve with the condition in order to still shoot up to your potential. If your experiencing it, chances are good that everyone else is as well so it's beneficial to be comfortable with making changes. If it were me I'd whip up some additional cross hairs with heavier wire and move to either some sort of adjustable rear aperture or make/buy some in larger sizes.
The center of a hole is still the center no matter how large the hole is. Don't be afraid to go big to get light back to the eye!
Hope this helped.
BTW, nice piece. Here's a "supa bling" silhouette pistol I did about 5/6 years ago for a germ up in Oregon. Nesika NXP action in 6.5BR Ware.