I think that is a misconception with some people surrounding line angles. Much like a river running down stream, 3-4 meters of rod over 100 meters, with a good line sag almost places you mainline on the deck for 20 meters. Most locations your casting into around 3-4 meters of water, so a 500mm trace with a float I cant really see it getting anywhere near the surface unless its substantially big and buoyant.

Personally I think having control of your rod and putting a bait exactly where you want is an important tool. Like whirinaki reef where you fish, you would know that that reef has crays and a decent sea life on it that will attract snapper from October when shelling ect... So getting your bait as close as possible would be the best advantage. Or Arapanui, putting your bait where the river mouth has soured out deeper hole when in flood, or fishing next to the foul. Or ocean beach, finding the calmest water for gurnard. Or kahawai, directly in the turbulence behind the waves...... Placing your bait exactly where you want it is an advantage. I think the experiment part is more on the rig itself. When you get a bait where you want it, what can you do to present you bait/baits in a way that more appealing. Like how can I clamp down a ledger rig that will cast well, and on impact with the water, maybe a design where a float holds the ledger upright off the bottom........ Maybe trying to have it so the rig is actually below the sinker............ Thats just an idea, but with the clips that are available now, you can get quite creative.

Another idea for your water column fishing is slidebaiting with non return clips and shaking the rod to push the bait out, your bait slowly jiggles to the sinker......