When the wind is at the ideal angle for highest speeds it is impossible to get back to the launching point in one tack on a speed board. It is also very rough in the channel. It takes a lot of energy to sail back, especially if you need to tack twice - or more. I have actually walked back faster up the end of the course than other sailors sailing over and back, only to hit the bank behind me. You only have to hit a bad wave and spin out, have a waterstart etc. and you waste a lot of energy for nothing.
So walking back part, or even all the way, is a strategy. For me this day, wearing 5kg of weight on my shoulders, it was very energy consuming trying to sail back upwind. I decided I would be in better condition for the good squalls if they came later if I walked half the bank to where I could sail back easily in one tack on flatter water.
The down side of this is you sometimes can't get as many runs and that can be a handicap in fluky conditions where more runs means more chance of hitting a good gust.
Two sailors (young blokes

) who took full advantage of the alternate strategy that day by sailing back upwind all or most of the time, Dave MacInnes and Chris Lockwood, had the fitness and skill to take advantage of it and it paid off for them with enough good runs to get a high average.
I may be wrong here, but it appeared to me that Tony Wynhoven was using a bit of both strategies and that also worked very well for him.