I've seen what Richard Noel does, leaving a gap between the top of the wax and the top bar
Some makes do not have the groove in the topbar and so cannot get into the head, but that is more common with vertically wired frames.
However that is guessing as I do not know what style Richard uses.
We prefer the grooved topbar and the foundation up into it....you do not get any 'flopping down' over the top wire when the wax softens that way....with vertical wires that is not a risk. However horizontal wires are most common in the countries like US/Canada, Aus, NZ which influence UK choices more than many European countries do. We prefer them as the pull is on the shorter sides which tends to cause less bending of the wood when the wire is under tension.