Based on the picture showing a steep dive of grade at the corner of the house, I'm concluding that there is substantial grade change within the back yard (behind the camera in the above picture.) That being the case, then there is plenty of "somewhere else" that the water can run in order to escape. We don't need to worry that wherever the water is going will fill up and start backing up into the swale. We just need to worry that the swale will handle the volume of water that is coming from uphill. I'm not in a position to do do hydraulic calculations for you based on storm intensity and duration, etc. I'm giving you my gut reaction based on what I can see and what I can imagine. I don't think your swale is large enough. It might work for many storms. But every so often, and we never know when, is going to come the doozy that makes everyone wonder if life-as-we-know-it, it over. You don't want water pouring into the basement windows then. I also think it's too close to the house. It's the path where water could be running for a substantial length of time (2 or 3 days). It would be better if that water was soaking into the ground 10' away from the foundation instead of 3'.

Another thing to think about is that if you can incorporate the swale into the yard such that its grades are gentle, then you can continue your landscape planting scheme uninterrupted by the swale. You can design planting beds and perform maintenance & mowing without concern of twisting an ankle or flipping a mower when you accidentally walk or drive into the steep side of a swale.

If you move the swale farther out and make it more gradual, it could conceivably hold several times as much water. You could begin at a slightly higher elevation next to the foundation in order to not have the window well top edges appear to be sticking out of the ground so far. So a little soil could go back against the house. I know grade is rising to the right but the picture doesn't show very far in that direction. I'm not sure what you'll be running into there or how much of the land is yours.

In the lower picture, I'm showing the swale profile running at capacity in order to compare the difference in volume of water carried. Your swale is the dark blue water. The other swale (light blue water) would carry all of yours plus about 4 X as much more in spite of being very little deeper.

I wouldn't want the bottom of the swale to be closer than 6' from the house. I'd prefer it to be 10' away.

On other subjects, it looks like you might could use a retaining wall somewhere near the corner of the house. I'd resolve that before creating the swale.

I don't know what trees you're planting next to the house, but they look like they may be too close.