What is the height of your sight line above your bore centerline? That affects the shape of the trajectory arc. A taller sight line makes the barrel angle up higher. That increased angle of departure means a lower velocity will hit the two impact points you describe. An estimate of velocity from bullet drop requires that information. It also requires the temperature of the day you fired to use the ballistic coefficient of the bullet accurately? What is your range's altitude above sea level, or, better yet, what was the barometer reading that day? These also affect the calculation.
For example, if your drop numbers were precise, and fired at sea level under ICAO standard atmospheric conditions (59 °F, 0% R.H., 29.921 in Hg), they would indicate about:
2040 fps for a sight line 2.0" above bore centerline
2094 fps for a sight line 1.5" above bore centerline
2148 fps for a sight line 1.0" above bore centerline
Note that the sight line is the center of your scope main objective or the top edge of an open iron sight like the Patridge sight.
Those velocity numbers seem low, even for an 18" barrel, given your powder charge. So I tried a different method: I took Hodgdon's 42 grain number for the 168 grain MatchKing, put it into QuickLOAD with that program's Varget model and adjusted case capacity to get the same 2520 fps velocity that Hodgdon measured for their 24" tube. I then cut the barrel down to 18" and got 2354 fps. Your gun probably shoots it a bit slower because the Hodgdon gun has a SAAMI minimum chamber and bore, as all SAAMI standard test barrels do. Your's might be 50-100 fps slower. I've seen 200 fps difference before, but that's less usual. Assuming your chamber is not as tight as theirs, let's say 2300 fps.
So, why would the drop be so high in your targets as to give a lower velocity result? Again, I don't know the conditions or even the COL of your load. But the most common cause of that error would be imprecise measurement of the differences in point of impact. These happen most often for a couple of reasons. One is that a lot of people shoot groups of just 3 or 5 shots, not cognizant of how much difference the center locations can sometimes have from one group that size to the next. The second common cause would be imprecise surveying of the range. Figure that for each 0.1" of measuring error on the target paper your velocity estimate could off 10-20 fps depending on how your errors combine. At the 200 yard end, the bullet is dropping that much every yard, so you can see how if someone surveyed what was actually a 100 meter and 200 meter range for different game rules, and just decided to call them 100 and 200 yards, things could go awry. And in fact, at a muzzle velocity of 2300 fps, it turns out that, for a 1.5" tall scope, the bullet is 1.5" high at 100 m and -4.5" low at 200 m.
Bottom line here is that you want at least 10 shots at each range, and I prefer 20 for this. If the holes start to touch and make the center location hard to find, put up several identical targets at each range, fire 5 rounds at the same corresponding aiming point on each, then find the average location above or below the aiming point for each target and then average these average locations. Do that for both the 100 and 200 yard groups. Putting more shots in each group makes your combined groups a little larger by allowing outliers more opportunities to show up, but the averages are more representative.
As for the range surveying, I actually keep a 100 foot tape in my car to check ranges against, if I'm uncertain about them. I then get actual numbers to work from.
