I have the test-plate pickled in Alum-salt-solution. So one can see better the effects.
On the left side ! used an 1mm Sterling Silver wire in form of an inverted U and a layer of low melting lead-bearing ivory-enamel. On the right the wire was formed in a little square. 
It seems, that with a thin layer of enamel the Eutecticum is better to control. While on the right the silver is more laminar molten.
If you want to try it and to hold the Eutecticum more under control, I would prefer to use a very, very thin layer of enamel and a thinner Sterling silver wire.
One could also try out the in form bended wires coat with holding agent, and powdering on a thin shift of enamel and the so prepared wire placing onto a copper sheet. I think, that could give the best control over the form of the eutectic-line.