Re: Russian Capture K98 kit
The curved sides on the sight hood are designed to fit into corresponding slots on the lower part of the sight base, thus securing it in place.
When fitted the sight hood should not appear to have the lower ends splayed out, but should be parallel to the sight base.
The front sight hoods and slotted front sight base were only fitted on rifles from late 1939 but not all rifles had these fitted, even later in the war.
If your sight base doesn't have the slots I'd advise against fitting the sight hood (a) because it will not be secure and, being strong spring metal can esily come flying off if knocked and (b) the hood is likely to start chewing up your finish and/or the sight base itself.
If you really like the look, maybe your smith can cut the slots?
Here's what it looks like when the slots are there:
Also look out for repro hoods, they are often made of thinner metal so, even when fitted, will rock back to front as they don't fill the slots out.