Using dynamic targets like <mo> or <tt> will occasionally cause a "miss target" and default to yourself but I've only noticed it happening when spamming single heal (Physick) for a period of time.
To remedy this, I use static targets and keep the tanks in the 2nd and 3rd party position. For everyone else I use <mo> Physick and just highlight their names in the party list.
It may seem excessive but you never miss and don't have to worry about targeting tanks.
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Code:
(Tank 1 heal)
/pac "Embrace" <2>
/ac "Physick" <2>
(Tank 2 heal)
/pac "Embrace" <3>
/ac "Physick" <3>