If possible, chronograph your load.
My old books show 20ish gr of 296 or H110 with a jacketed 240gr slug put you in the 1100fps range. And I don't think today's powder is quite the same as what was in the books 20-30 years ago...
The slower the bullet is, the higher on the target it will print. Sights scaled for full house loads may not have the adjustment for a light load, and that is what I think you are seeing here. Even if the load seems "peppy" to you.
Get your load clocked, and see what it really is doing. Once you know that, you can make informed decisions how to proceed.