The real first question is, "How are you aiming?".
Are you lining up the three dots and putting the dots on the target at center or 6 o'clock?
Are you lining up the top of the sights and putting the top of the sights at center or 6 o'clock?
Or are you lining up the dots but aiming with the top of the sights at center or 6 o'clock?
On my 40VE, when the dots are lined up, so are the "iron" sights (they're plastic). I tend to line up the dots but then put the "iron" sights at the 6 o'clock position on the target and I will consistently shoot about 8" low at 25 feet.
When I measured the factory front sight I got the following results:
Top of sight .185"
Top of dot .170"
Center of dot .125"
At Brownell's they sell a tritium front sight for a Sigma V that they say is .160" and made by S&W
SMITH & WESSON : NIGHT SIGHT, FRONT, .160" - World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools - BROWNELLS
I'm buying an Ameriglo front sight from GlockWorld that they say is .165 - standard for a Glock. I expect to file the slide insert down to fit the Sigma as in the HI-VIZ fix. The problem is that I don't know where they are measuring that height. I think that is the top, which will be .020 lower than my Sigma factory sight.
Ameriglo Sights & Lasers ameriglo tritium metal front sight - GlockWorld.com
If you go to the Ameriglo websight, they sell plain black Glock front sights in .165" to .350" height for $20-25. They say that Glock standard is .165.
AmeriGlo Weapon Sights | Front Sights
Well, if I was shooting in daylight and using the top of the sights in daylight, and I didn't want a HIVIZ or AmeriGlo sight, I would just take an emery board (fingernail file) to the range, black out the front dot with a Sharpie, and alternately flat-file the top of the factory sight and shoot until the POI was where I wanted it. You would black out the front dot because, if you are filing the front sight down and aiming with the top of the sight then the front dot will not align with the rear dots when you are aiming and the front dot would be distracting.
Bottom line, this isn't a target pistol. In most self-defense situations you will be closer than 25 feet and you're not going to be lining up a three-dot sight. It won't matter if the sights are a few inches low. I'm getting that AmerigGlo sight so that I can acquire the front sight in a low-light SD situation. I think that rear Tritium sights would only get in the way under stress. Just IMHO.