Just out of curiosity, did you mean your temps were better when the fans were set to intake air from external, through the radiator, and into the case? Did you have any other case fans exhausting air out of the case?
I'm currently in the midst of transplanting my old PC into a SFF casing and have an EK AIO waiting to be installed, and I couldn't decide which way to set up the fans, ie.
1) Positive Pressure: 2x 140mm fans drawing air from external, through radiator, into case, and 1x 140mm fan exhausting on top. I believe this is the more traditional way of planning the airflow as the coolest air is used to cool down the radiator.
2) Negative pressure: 2X 140mm fans drawing air from inside the case, blows through radiator, exhausting air outside the case, and 1x 140mm fan exhausting on top. This too feels like it could work as cool air will be drawn into the case via mesh on 3 sides and exhausting on the remaining 2 sides? Only issue I have with this configuration is that I cannot fit the fans between the rad and case panel as the AIO(vertical layout) hoses are in the way, so the fans will have to be "blowing" into the rad instead of drawing air through the rad.
I will be running some tests when I get the chance, just trying to get some idea which might have a higher chance to perform better so that I can do that option last to save me the hassle of switching back to an earlier option as I will also be testing the varders vs some old noctuas I have from my old rig.