When soldering both plumbing and wiring I have heard the advice that you shoulf apply solid solder opposite to your heat source, since the solder "will flow towards the heat" once it melts.
Is this a true statement, in general?
I could imagine that perhaps an increasing temperature gradient would decrease the solder's viscosity, and maybe that could promote more flow?
(And obviously a really uneven temperature could leave areas below the melting point, so in that case the advice sort of makes sense but only in a trivial way.)
I can think of other reasons why you might want to apply solder away from the heat source - in particular so the heating device doesn't get in your way. Also because by applying the solder far from the heat source your have a high likelihood of the melting temperature being exceeded throughout the joint once it melts at the solder. I wonder if there are the only genuine explanations.