|Sorry for the delayed response. Glad to hear you managed to duplicate the results. I used a span of 10MHz for the test, where RBW and VBW ratio was 100. This should not affect your results nonetheless, since the signal level should still be far above the noise floor of your analyzer (and no close proximity signals should be present for the need to separate them). Reference level was 20dBm with 30dB attenuation (wrong settings for these could indeed affect your signal level).
RBB tab settings are not important in your case, since these actually control the analog filter for the receive chain (not transmit).
Tweaking bias settings can indeed help to push the output power value higher, but bear in mind, that you are only increasing DC value at this point - at normal operation you would be oversaturated and driving the chain in the non-linear range.
+10dBm is the realistic output power for a modulated signal (not CW) that can be sent without distorting the signal.