I installed a Diamond X-200A antenna just above a Thunderbird TH5MK2
tribander. Due to a short mast, the Diamond is virtually sitting on top
of the Thunderbird.

The lead-in consists of some 20 feet of 9914f and 50 feet of 9913,
connected with UHF connectors.

The measured SWR minimum is at 147.7 MHz and 1.2:1 at the far end of the
coax. The MFJ 259B reads 1.9:1 at 144 mHz. Presumably the SWR is a bit
higher at the antenna connector.

If I use a longer mast to raise the Diamond above the tribander, can I
expect the resonant point to move to the specified 146 MHz and the SWR at
144 to go down? How much separation is needed?