From my experience in maginal wind relaunch, I can relaunch it with lower wind when swimming back punctually rather than sitting on the sinked foil. Maybe it is due to my light weight and I can't sink the foil deep enough but it happens sometimes that the little downwind drag when sitting on the foil was killing the relaunch. While free of hydrofoil I can swim backward with punctual hard energy to start getting it out of the water.
An second point when you have 4-5 knots average and punctual 7 knots gust : you can relaunch the kite in gusts but you cannot bodydrag downwind in 4-5 knot toward the hydrofoil. Indeed the hydrofoil goes downwind at about 2 knots while your kite cannot hang in the air (even with loops) in 4-2=2 knots related wind. So the hf drifts faster than you, whatever your bodydrag technics. My feeling at least. Hence the leash.