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Lots of chatter.

First. Changing the pressure the system operates at will have absolutely no effect on the heat distribution at all. None. Zip. Nada. 20 psig is ample, and it would probably be just fine at 15 psig.

Second, as @hot_rod points out, your problem isn't flow rate through the piping. You are getting an entirely reasonable delta T. So there's not much point in worrying about that.

Third, you are getting a reasonable input temperature to the loops. The near boiler piping isn't ideal, perhaps, but it works so leave it alone.

Fourth. The bad news. The floor arrangement, as installed, simply isn't capable of pumping enough heat into the room to keep it warm. Furthermore, spoiler alert, raising the input temperature enough to do so will damage that flooring as well as giving you a hot foot. A wood floor should not be run over 80 F, so even if you had piping which made the floor temperature reasonably even you couldn't get more than 20 BTUh per square foot out of the floor, regardless of input temperature. So raising your input water temperature isn't going to hellp.

You have a design which simply won't work. They happen.

The solution, though, isn't rocket science either: as has been suggested, additional emitters in that space. I'd suggest panel radiators. They aren't unattractive, they don't take up much floor space, they work well with the water temperatures you are working with, you can get beneath the floor to install the piping… What's not to like?

Can't quite make it out, so I'll have to ask. Where in the circuit does the expansion tank and automatic feed valve tie in? And what pressure (looks like about 15 psig?) is the tank and feed set at?

What I'm concerned about is that the noise may be cavitation at the inlet to the pump. Whether this might happen is related to what is between the point of constant pressure at the tank and the inlet to the pump.

By the way — nice neat job of putting it together.