Yeah, clearly "file" was incorrect.
You could squeeze the sight in a vise to make the post larger, then file/shape it to suit.
What about a P38 sight? I've never seen one in the flesh, but I think they share the Luger's dovetail, and maybe they come in different heights?
I found this on a Walther forum, applying specifically to the P1, which may not be the same as a Luger/P38 but it's a start.
"If you are shooting low, go one number higher. Shooting high go one number lower.
My P1 shoots about 1 to 2 inches low at 25 feet, has a #3 front site.
So I ordered a #4 from Numrich. Looks like 15/100 difference between each sight. All the other vendors play dumb, just list front sight.
Walther P1 Front Sight Numrich
Front Sight, #5, w/ White Dot, .210" High
Front Sight, #4, w/ White Dot, .225" High
Front Sight, #3, w/ White Dot, .240" High
Front Sight, #2, w/ White Dot, .255" High
Front Sight, #1, w/ White Dot, .270" High."