It has more than just sea lanes. There are air land and sea routes to Yemen
Beyond that, Iran has invested huge amounts to localise production capabilities across the Axis of Resistance, so that they are less reliant on Iran. We already know IRGC has a presence in Yemen, likely to assist with localised production / training / tactics / military operations generally.
Iran also has 2-3 navy support/command/intelligence ships permanently stationed near Yemen, likely that these are providing constant stream of intelligence/monitoring data to Yemen to assist in operations