It is likely that Russia would deploy S350 or S400 around capital assets.
Previously in Syria, Russia has supplied S300 and earlier systems purchased by Assad, they have just finished delivery of the last S300's.
Up to about a year ago, Israel would strike and disable or destroy those Syrian manned systems when they needed to overfly Syria for defensive strategies.
Russia stayed out of these incidents, and Israel maintained defensive control.
Recently, Israel has ceased these airstrikes as the Syrian situation deteriorated and destabilized. Israel has not made statements regarding cessation, and maintains an apparent good relationship with Russia. It may be a sign that Russia will defend Russians when in Syria.
Gets complicated.