I don't know if I'm experiencing a "senior moment", but I can't make sense of something & am hoping one of you gentlemen can de-confuse me please.

Yesterday I decided to take my recently acquired alte Frau, a 1931 Haenel IV fitted with a BSA
19a thin ring & blade front sight to the club & try her out over longer distances than my little garden range will allow. At my home 8 yards maximum I needed a bit of hold under, as expected, so I thought I'd make a crib sheet out to 30 yards & then go and have some fun on the HFT course, trying to hit the plates. This is where my confusion began when I discovered the hold under increased with the distance to the target, rather than decreasing as I'd expected - thus
10 yards 2" hold under
20 yards 4" hold under
30 yards 8" hold under

The rear sight is wound right down as far as possible, raising it increased the hold under needed to hit the target card, as expected. The rotating front sights, blade & ring, both give the same impact point, when set in the correct upright position.

Am I losing me marbles or does this lovely old girl defy the laws of gravity?
Yours in confusion,
Glyn