In the booklet (TT), or sheet of paper (ASP), that came with the engines I own; both TT and ASP list 11x7 as the recommended prop for break-in and general usage on their .61 two strokes.

Is the manufacturer wrong? Maybe yes, maybe no.

I know the 12x6 and 13x4W worked well on my trainer; and the 11x7 didn't work the way it needed to for that particular plane.

A fellow club member took one of my 13x4Ws and tried it on a 61FX and hated it.

Prop selection is one area of RC where there is no shortage of opinions. What one person thinks is good performance; the next person may think it sucks.