You're going to have a lot of weird balance issues now. What I would have done was just divided the WPP you get at 30 (250), that gives you 111WPF in one category by 18 agi (which is your target balance build). This way, once you hit 18 WPF, you have the baseline singular WPF.
Now, what about high agi builds? Lets examine the most extreme case a 3/36 builds. It would have 500 WPP. That could be a 111/111 split, or 145 with no WM. Let's say he gets 1PS, PT or PD and 12 atheletics. With only enough left for 10WM, sure, he will have just over 200 singular WPF. But with only 1PS, he will not be effective. That build would have 189 WPF with the current system, ~20 WPF will not make a big difference.
On the other extreme, at 36/3 or whatever -/3, you will have 55 WPP which is around 41 singular WPF. With 1WM, they'd then have 61 WPF.
Now let's look at some more balanced scenarios.
24/15 would get about 101 Singular WPF from agility.
18/21 would get 118 Singular WPF from agility.
15/24: 125
12/27: 130
9/30: 134
You should also take in to account that this would not give players higher than level 30 even more WPF which we have in the current system.