I asked KataGo to estimate the komi value of handicaps on different board sizes.
This is what it says (Japanese rules and standard placement of handicap stones):
9x9
h1 = 5.5 komi
h2 = 15 komi
h3 = 24 komi
h4 = 45 komi
h5 = 71 komi
so roughly 15 points per full handicap stone
13x13
h1 = 6.5 komi
h2 = 18.5 komi
h3 = 30 komi
h4 = 44 komi
h5 = 51 komi
h6 = 63 komi
so roughly 11 points per full handicap stone
19x19
h1 = 6.5 komi
h2 = 19 komi
h3 = 31 komi
h4 = 46 komi
h5 = 59 komi
h6 = 74 komi
h7 = 87 komi
h8 = 102 komi
h9 = 112 komi
so roughly 13 points per full handicap stone