Question about bonus modifiers when leveling up Options

[Olav]

How many skill increases are necessary to get a +5 bonus modifier?

I'm trying to raise my strenght attribute, and between each level I fight a lot hand to hand and with blunt weapons just to get as many strength bonus points as possible. Both of those are minor skills, while blade is a major skill, which I also normally increase 2-3 points for each level.

I think during my last level I gained 6 hand to hand points, 5 blunt and 3 blade points, but still the bonus modifier was only +2.

Again, how many skill points are necessary to get +5 points?