This is an interesting observation. I have beacons on the air using the Arduino and SI5351A and am interested in trying to duplicate your test.
I have some questions regarding your test setup;
Where in your circuit did you place the current meter?
Did you use the same Arduino in each test?
Did you use the same SI5351A chip/circut/level converters?
Did you use the same meter in each test?
Thanks in advance for the extra info.