Fast question on HP and Fatigue house rules

[Jesster]

Hey all,

Long time GURPS player, trying to move to 4th ed. Reprogramming GCA 4 with some house rules and having a little problem.

HP in our house rules is ST+(HT-10)/2 (so you get one extra HP for every two HT above 10.
Fatigue is the opposite stats (so you get one extra Fatique point for every two ST above 10).

In GCA I put in these lines
Hit Points, basevalue(ST:ST+((ST:HT-10)/2)), step(1), maxscore(1000000), minscore(0 - me::syslevels), up(2), down(-2), symbol(HP), mods(Size HP), mainwin(5), display(no), disadat(-1), initmods(Size, -10%, group(Size HP)

For some reason, when I increase ST, it puts too many points into HP and actively spends some levels into increased HP. For example when I set ST 15 it sets HP at 21 (and auto spends 10 points into extra hit points) and sets Fatigue points to 19.5 (and auto spends 15 points into extra fatigue). Now I know I need some @INT (integer) setting in the line so I don't get a .5 stat, but I don't know why it's auto spending points.

I'm thinking it's that minscore value but I don't know much about GCA4 and so that 0-me::syslevels thing is new to me.

Help?

-Jesse