This is about what I would expect from a Manchego. I shoot for 5.2-5.4.
During pressing the bacteria continue to convert lactose to lactic acid, so it is normal to see a pretty good pH drop overnight. This is in direct relationship to the pH at draining and hooping. i.e. If you had let the curds get down to say 6.0 then your final pH might be in the high 4's. The TA-61 has a longer pH curve that kicks in about 5 hours into a make. But that's a matter of timing not necessarily associated with the finished pH. TA contributes very little during the early stages of acidification, so it's important to also use a Meso that will acidify earlier and give the flavor profile that you want.
If you want a higher pH cheese then reducing all starter bacteria just a little would help, but the pH at draining (pitching) and hooping is just as important.
The pH at de-hooping also depends on a lot of environmental factors besides just the bacteria. The temperature of the room and the length of pressing time are 2 things that can drastically change a cheese. Warmer rooms = more active bacteria = lower pH. Cooler rooms will produce cheeses with less of a pH drop. Longer pressing times without cooling and brining also gives bacteria more time to produce extra acid. In order to hit absolute pH targets, you would have to get up in the middle of the night and take readings.
You also have to consider the calibration and accuracy of your pH meter.
