Hi Joe, I do have the the same result and pictures as you have and having in hands FT-950, and 2 SDRs all 0,5 m away from mBITX.
But with oscill parallel to dummy load you can get
carrier level as -26 /-30 dB(my results) or even better. Allison has good understanding and hope she is right. But still for me hard to get how to solve the problem in practice. Go out to band with such SSB signal or use PA is not good idea. But still I like not noisy receiver! The idea is good but may be PCB layout and Si5351 has someting?
George UR4CRG/RX3ARG( sorry for no pictures I am not good in PC)