Are some engines more susceptible to ground plane issues than others?

There is no "adjustment" to make, other than making sure both handrails are connected to the antenna lead and they're not grounded to the shell. The antenna is all important as far as the signal is concerned, it's what receives the signal radiated by the electrical ground wiring and any added "earth ground" wires.

FWIW, I've found that some K-Line TMCC engines were more sensitive to signal issues under my second level, I ran an "earth ground" line around under the deck and all is well.

Thank you John,  please excuse my ignorance. I am a CE not a EE.  Is there a method to measure earth ground strength or its ability to block signal interference at different areas on the layout?

Well, there really isn't some concrete signal measurement technique.  The folks at the NJ-HR club came up with a signal measurement car that had a Bluetooth meter that the drove around and watched the signal on a smart phone.  The R2LC TMCC receiver has an FM receiver that does have an output that can be monitored to indicate the incoming signal strength.  I've attached a document that was written, I believe, by Bob at the NJ-HR about their rig for checking signal strength.

TMCC Track Signal Test Car with Bluetooth.pdf